Mousetrap Car Report: Reflection Blog -- Mar.

OUR MOUSETRAP CAR'S NAME IS VELVET.


Here we are! Look below:

SPEED OF CAR AND PLACE IT CAME IN:

Our car, VELVET, went further than 5 meters, approximately 8 or 9 meters.

When we did the official trial, Mr. Rue timed our car to go the 5m in 2.84 seconds!!

The speed of Velvet can be calculated by using the simple formula: distance/time.
      ~ Distance/Time
      ~ 5m/2.84s = 1.761 meters per second.

Out of everyone's official times, (of all 3 class sections), Velvet was the 2nd fastest. Of my class, A-block, it was the fastest. Good job, Velvet.


PHYSICS OF THE MOUSETRAP CAR:

A.)

• Newton's 1st Law: The more mass an object has, the more inertia it has. Velvet was fairly lightweight, so it was easier (less resistance) for the car to start moving. 

• Newton's 2nd Law: Acceleration = Fnet/Mass. The lesser the mass, the more it accelerates. Velvet had a small mass, so it had a greater acceleration at the start!

• Newton's 3rd Law: Every action has an equal and opposite reaction. As the CDs were in contact with the ground, the relationship reminded me of the "horse and buggy" topic. The CDs had friction wight he ground, so it allowed for the car to actually move forward.

B.)

• The static friction between the bottle cap axles and the fuzzy hangers: the car has resistance on the axles and body to start rotating while currently at rest. 
• The other is the kinetic friction caused by the CDs and the ground: the car has resistance when the car is stopping its movement.
• Kaylee and I had a problem with the front wheel. At first, the hangers were pushed too close together, causing the bottle caps and metal rod to turn with a lot of difficulty. Velvet's issue was solved as we re-glued the hangers further apart.
• With no friction at all, Velvet's wheels would not have rolled. Kaylee and I used a balloon to cover the CD wheels in order to produce traction with the ground! A great advantage!

C.)

• We only had 3 CDs. Because of this lack of materials, Kaylee and I decided to make a tri-pod car. We used CDs because they are perfectly circular, and they were big in size. The bigger the radius of each wheel, the further the car travels with each revolution.

D.)

• The conservation of energy is where energy cannot be created nor destroyed...it is merely transferred into another form. Energy = the capacity for an object to do work. 
• The energy could have been transferred into heat, sound, and/or vibrations. When Velvet moved, not all of the work input was equal to the work output. 

E.)

• Though we had no extended lever arm, the mousetrap metal lever provided a very short one. The string that was attached to this "lever" was a certain distance from the spring. This created more torque (rotating force). *Torque = Force x Distance
• The lever arm of the metal spring (the actual trapper of the mice) was pulled backward to load. As the metal rod was let go, the string was pulled. This pulling force allowed for the back axle to rotate, causing the wheels to rotate as well. The bigger the lever arm, the more torque.
• The power output of Velvet was the work done/time. The power could be calculated if we can figure out the total work done. I cannot.

F.)

• Rotational Inertia (RI) is the inertia a rotating object has, but is not dependent on how much mass that object has, but where it is distributed. When most of the mass is located furthest from  the axis of rotation, there is more RI; when most of the mass is located closest to the axis of rotation, there is less RI. Velvet had a relatively small RI because the mass of the CDs was spread out, but the hole in the middle of the CDs gave Velvet that little "umph."

• The more rotations the CD makes per time interval means that Velvet had a big Rotational Velocity (RV). The bigger the CD, the less rotations it has to make in order to cover a large distance.

• The Tangential Velocity (TVel) of the CD is simply distance/time. But, the inside ring of the CD has a smaller TVel because it covers less distance than that of the edge of the CD.

G.)

• The spring does no work on the car because the force it uses to propel the car is not parallel to the distance in which it travels. 
• The potential energy (PE) cannot be calculated because it is not at a specific eight. It is on the ground. The PE must be a constant 0 joules. The kinetic energy (KE) cannot be calculated because the velocity is unknown and changes over time. KE = ? joules.
• The force of the spring cannot be calculated either. This is due to the velocity. We don't know the velocity, or the distance, at which the spring "spring" so the force is unknown.

PICTURE OF VELVET:

I don't know if you can see it completely, but Velvet was outstanding!
The bottle caps supported the CDs on the axle (metal rod).
The mousetrap was securely fastened on the hangers with hot glue.
The string was wrapped around the back axle rod, and tied to the lever arm part of the mousetrap.
The balloons were wrapped around the CDs to created traction on the ground.
The big paper clips were flattened, (Kaylee hammered them!), and glued to the hangers for the body's support.

That was all! Simple but sturdy.



REFLECTION:

• Our original design was a 4-wheeled wooden car, that included 2 large wheels and 2 small wheels. Our axles were going to be flattened paper clips. Our final design was much more efficient, because we used 3 wheels of the same size, and felt hangers for the body (less mass). When Kaylee and I researched more online, we found that these changes were beneficial and ultimately made our car better in all.

• Our major problem was the front wheel. The bottle caps were not completely aligned, so the wheel and the car veered to the right every time we did a trial run. To fix this, I drilled the hole in the hanger lengthwise, so that when I hot-glued the metal axle rod onto it, the CD would then be straight. It was successful!!

• To make Velvet faster, if I did this project again, I would make a lever arm that snapped quickly when the mousetrap was let go, in order to maximize the pushing force. Also, I'd use a thinner string so when wound up, it would not get caught.

A VIDEO OF OUR RACE: BUT NOT THE OFFICIAL, FASTEST ONE:



Again-- 2.84 seconds. I'm so proud. 
Thanks Kaylee for being such a great partner!!


CHEERS.

Unit 5 Blog Reflection -- Feb.

PART A: WHAT WE LEARNED

A1.) What is Work?

A2.) What is Power?

A3.) Kinetic Energy/more work

A4.) Potential Energy

A5.) PE and KE relationship

A6.) Machines

A7.) Extras

A1.) What is Work?

"Work is the effort exerted on something that will change its energy" (Hewitt 102).

• Work = force x distance
• The work will be doubled if one or both of these is doubled. They are directly proportional to work.
• Work has two categories: work done against another force; work done to change the speed of an object.
• Work cannot be done if the force and the distance are not parallel. They must be parallel.

The unit of measurement for work is JOULES, or (newtons)(meters).

A2.) What is Power?

"Power is equal to the amount of work done per time it takes to do it" (Hewitt 103).

• Power = work/time
• Work is directly proportional to power, so if the work is greater, the power is greater.
• Time is indirectly proportional to power, so if the time interval is smaller, the power is more; if the time is bigger, the power is less.

The unit of measurement for power is WATTS, or (joules)/(seconds), or (newtons)(meters)/(seconds).

A3.) Kinetic Energy/more work

"Kinetic Energy of an object depends on the mass of the object as well as its speed. It has energy of motion" (Hewitt 106).

• KE = 1/2(m)(v)^2
• Mass and velocity are both directly proportional to KE.
• An object cannot be at rest and have KE, as we know that KE is energy in motion.

The unit of measurement for Kinetic Energy is JOULES, or (newtons)(meters).

• Work = ΔKE
• Example: when an object goes from not-moving to moving, its KE is changed...and work was done on it.

Here's my podcast below:

Wyatt throws the snowball with a certain force, which gives the ball velocity and goes a certain distance. The ball gains KE.


A4.) Potential Energy

"Potential energy is...energy that is stored" (Hewitt 105).

• PE = mgh
• PE = (mass)(gravity)(height)
• PE = (weight)(height)
• These are all variations of the formula. Potential energy only exists if the object has mass and is at a certain height.
• An object can have PE if it is moving; (in mid-fall).

A5.) PE and KE relationship

This picture shows how PE transfers into KE once the man falls (loses height, gains velocity).

**Let's fill in the blanks: both the kinetic and potential energies must add to equal 10,000 joules.

10,000 joules PE

 0 joules KE

7,500 joules PE

2,500 joules KE

5,000 joules PE

5,000 joules KE

2,500 joules PE

7,500 joules KE

 0 joules PE

10,000 joules KE

A6.) Machines

"A machine is a device for multiplying force or simply changing the direction of force" (Hewitt 110).

• Work input = Work output
• (force)(distance)in = (force)(distance)out
• F x d = F x d

~ Machines only simplify the amount of force needed to put into a system over a larger distance. The force output is multiplied. The terms are indirectly proportional.

~ Conservation of energy for machines: The work output cannot exceed the work input. Energy cannot be created nor destroyed. Both the work in and work out must be the same!

An ideal machine would have 100% of the work input appear as the work output. 

But...whenever some energy is transformed from one form to another, (into heat, sound, vibrations, etc.), we say that the machine is inefficient.

A7.) Extras

You carried a computer down the street for 20m. How much work did you do on the computer?

• None. The force and distance aren't parallel! Gravity is the only force on the computer, and it is pulling downward.

I am running up the stairs. I weight 20N, and the staircase is 12m high vertically. How much work did I do by running up the stairs?

• Work = force x distance
• Work = 20N x 12m
• Work = 240 joules

Do I generate more power if I climb the stairs in 10 seconds or 20 seconds?

• Power = work/time
• Power = 240 joules/10s = 24 watts
• Power = 240 joules/20s = 12 watts
• Less time is more power!

A ramp is 1m high vertically. The length of the ramp is 3m long. You are trying to lift a box that weighs 30N into a truck. 

~ If you use the ramp the 1st time, show how it is easier. 

~ If you don't use the ramp the 2nd time, show how it is harder.

• (force in)(distance in) = (force out)(distance out)
• (10N)(3m), with ramp = (30N)(1m), no ramp
• The force input is the push/pull up the ramp; the distance input is the distance win which you pushed/pulled the box; the force output is the weight of the box; the distance output is the height of the truck.

A car is moving at 20m/s speed and requires 10m to stop. How many meters will it take to stop if the speed of the car is 40m/s?

• KE = 1/2(m)(v)^2
• 1/2(m)(20)^2 = 10m (given)
• 20^2 = 400
• 1/2(m)(40)^2 = ?
• 40^2 = 1,600
• Because 1,600 is four-times the velocity, because it is squared, we can use the formula:
• Work = ΔKE
• (force, constant)(distance) =  4x the ΔKE
• (force)(4x the distance) = 4x the ΔKE
• So...the distance required is 40m....which we found my multiplying 10m x 4.

A roller coaster can go up a large hill, small hill, and a medium hill in that order. Once released, the coaster only moves due to the law of physics. Why are the passengers able to complete the ride?

• Because energy cannot be created nor destroyed, the PE of each hill transfers into KE once it falls. When it begins to climb a hill again, the KE transfers to PE, and vice-versa, allowing for the coaster to continue traveling once it goes over each hill individually.

PART B: REFLECTION AND GOALS

What I've found difficult about this unit is the last topic we studied: ramps. I understand the problems and have contributed in class, but I needed more time to study it.

I overcame this difficulty by using my quizzes and notes to re-write the answer and descriptions of each term and each problem we did together. It helped be see physics not just on paper, but also in my head.

My effort in this class has been right on target. (I wish my class was more focused though). I typically do my homework and participate every day, because the material is interesting and my classmates are fantastic! The formula/problem-solving questions are fine for me; I do each step carefully and end up with the right answer (unless I did math wrong or didn't have persistence!)

My goal for the next unit is to be better organized with my quizzes and other scattered papers. Right now, I have everything in my spiral notebook and the inside cover of my binder. Also, I want to start doing more things with other people in my class, that I don't typically talk to every day. I am excited for the next chapter!

~Connections: 

1. The string that pulls my window blinds up and down sometimes sways and I think about the pendulum bob.
2. Walking/running up the stairs makes me think of doing extra work :(
3. When I carry my blue Star Wars water bottle around-- I'm not doing work! Not parallel!

CHEERS.

Machines -- Ch. 7 Resource

Paul Hewitt talks to his students about a pulley (why it is a machine).

He says "and that piano is going up in the air. How can be such a thing? Well first of all, if the pulley system means that the piano is being held by ten ropes...he's pulling one of those...so he's got one-tenth the weight of the piano on every rope -- the one he's pulling!"

Watch and learn WHY we can use a pulley to lessen our workload input:



On the chalkboard behind Hewitt, it's written that WORK = Δ ENERGY

• Work = force x distance
• Machines: Work input = Work output
• (force)(distance)in = (force)(distance)out

The force input is the amount of force you use to push/pull the object.
The distance input is how far you push/pull when you exert the force on it.

The force output is the original weight of the object.
The distance output is how far the object actually goes when the force acts on it.

ENERGY CANNOT BE CERATED NOR DESTROYED, THEREFORE YOU CANNOT GET MORE WORK OUT OF A MACHINE THAN YOU PUT IN. 

A MACHINE SIMPLY DISTRIBUTES THE FORCE (INPUT) OVER A LARGER DISTANCE, MAKING THE WORK INPUT EASIER.

THE WORK IN AND WORK OUT MUST BE EQUAL!!


CHEERS.

Work & Power -- Ch. 7 Resource

TED-Ed: Lessons Worth Sharing.

Peter Bohacek's lesson and Luke Cahill's animation created this educational video about how work/power....works. What is it? How are these scientific terms related?

Watch it. Learn it. Enjoy it. Share it.




**The video is helpful! TED-Ed uses a clock to explain each concept.

WORK: "the effort exerted on something that will change its energy" (Hewitt 102).

• But that's a bit complicated. Let's say that WORK is just the exertion for force on an object for a certain distance. Work is also a transfer of energy.
• In the video, the clock's metal cylinders were moving up/down; the force applied to the cylinders had to be PARALLEL to the distance at which they were moving. Work cannot be done if the force and the distance are not parallel.
• Work = Force x Distance

POWER: "the amount of work done per time it takes to do it" (Hewitt 103).

• Power has to do with time. The more time it takes to do work on an object, the lower the power. The less time it takes, the more power! 
• Work is directly proportional to power; time is inversely proportional to power.
• Power = Work / Time

So the TED-Ed video gives us a better understanding of work and power. I hope this cleared up any confusion that you may have had beforehand. See you later!


CHEERS.

Unit 4 Blog Reflection -- Jan.

Part A.) WHAT WE LEARNED

1.) Circular Motion (tan/rot Velocity); Gears; Train
2.) Rotation Inertia & Angular Momentum; Hoop/Ball
3.) Conservation of Momentum; Skater; RI versus RV
4.) Torque
5.) Center of Mass & Center of Gravity; Sports
6.) Centripetal Force (and centrifugal)
7.) Extra Problems to Consider


A1.) Circular Motion (tan/rot Velocity)

Linear Speed is exactly the same as Tangential Speed. The equation in words is "the direction of motion is tangent to the circumference of the circle or rotational axis per time interval."

• Formula: distance/time

Rotational Velocity is completely different. It is the amount of rotations an object or system makes in a certain time interval.

• Formula: rotations/time

Two things can have the same tangential velocity but different rotational velocities.  Two gears may cover the same distance over a period of time, but they don't have the same # of rotations.
A smaller gear would have to rotate maybe twice as many times as the big gear rotates to cover the same tangential distance.

Similarly, train wheels keep a train on the tracks --> The wheels are slanted with the bigger (larger radius) side on the inside of the track, while the smaller side is on the outside. This makes the larger side have a higher tangential velocity because it has to cover more distance to catch up.
The wheels will tend to rotate towards the middle of the track; the larger side covers more distance per revolution and it turns. They re-align and on turns, the train can straighten-up.


A2.) Rotation Inertia & Angular Momentum; Hoop/Ball

Rotational Inertia is a branch of inertia that states an object will resist change in rotation, whether it be to start or stop the rotation.
What determines how much inertia an object has is the distribution (position) of its mass. When more of the mass is further away from the axis of rotation, there is more inertia; it will be harder to start/stop its spin. When the mass is closest to the axis of rotation, the object will be easier to start/stop its spin.

The hoop and ball: Explained here in this podcast video, a hoop and a solid cylinder race down a ramp. Both have the same mass and radius. Why does the hoop lose? Look below!


 
Angular Momentum is the rotational inertia multiplied by the rotational velocity of an object. These terms are inversely proportional, so as one gets big, the other gets smaller. Vice-versa.

• Formula: RI x RV

A3.) Conservation of Momentum

The conservation of momentum occurs when an object is rotating, such as a ice-skater. Let's say that she has her arms out, and suddenly pulls them in toward her body. What happens?
At first, her arms are far from her axis of rotation, so she had a high rotational inertia and a low rotational velocity (formula).
But as her arms go in, she spins faster! Her rotational inertia is low and so her rotational velocity must get higher to compensate for the change. As one goes up --> the other goes down.

In this picture, the "I" stands for rotational inertia. The "w" stands for rotational velocity.

BOTH girls in the picture has the same angular momentum because RI x rv = ri x RV.

A4.) Torque 

Torque is a force that causes rotation. 

• Formula: force x lever arm

A force is a push or a pull on an object.

A lever arm is just the distance between the force-action and the axis of rotation. The lever arm is perpendicular to the force.

So as the formulas shows us, the force and the lever arm are directly proportional. Whichever gets larger helps raise the torque and cause a rotation of some sort.

Let's do a torque problem: There's a 2N ball and a ball that is 3N resting on a balance with a fulcrum in the center. The 3N ball is 4 meters from the axis of rotation. How many meters (how long is the lever arm) is the 2N ball from the center?

clockwise torque = counterclockwise torque
(force)(lever arm) = (force)(lever arm)
(3N)(4m) = (2N)(x)
x = 6 meters


A5.) Center of Mass & Center of Gravity; Sports

Center of Mass: the point where the average distribution of mass is located on an object (the middle usually).

Center of Gravity: the point where gravity is pulling down an an object.

Base of Support: the foundation on which an object is located, right above the support force.

Why are football players less likely to be pushed over when they keep their legs should-width vs. feet together? 
~ With legs further apart, the base of support is widened, giving a larger foundation for the object. It is harder for the center of gravity to go beyond the base of support. When it does go over, however, the object will fall.

Why are wresters told to bend their knees when wrestling?
~ They bend their knees so that their center of mass is lower to the ground (and base of support), so it is harder to get the center of mass beyond the base support and it would be unlikely for the wrester to fall over sideways.


A6.) Centripetal Force (and centrifugal)

Centripetal Force: center-seeking force (toward the axis of rotation).

Centrifugal Force: center-fleeing force; it is FICTICIOUS (away from the axis of rotation).

This image is of a ball rotating in a circle. The centripetal, centrifugal (fictitious), path of inertia (tangent line), and center are all labeled.

A7.) Extra Problems to Consider

• Bus problem: you hit person next to you as the bus turns a sharp left...why?
• Satellite: is the satellite stationary above earth? How do the forces/vector quantities keep it in orbit?
• Why does water fly out of a washing machine? Is the water moving on a curved or straight-line path?
• Why are racetracks banked with one edge higher than the other? Where is the centripetal force acting on it? Add vectors to prove your answer.

Part B.) REFLECTION AND CONNECTIONS

What I've found difficult about this unit is the last topic we studied: centripetal force. I understand the problems and have contributed in class, but I needed more time to study it.

I overcame this difficulty by using my quizzes and notes to re-write the answer and descriptions of each term and each problem we did together. It helped be see physics not just on paper, but also in my head.

My effort in this class has been right on target. I do my homework and participate every day, because the material is interesting and my classmates help each other. The formula/problem-solving questions are fine for me; I do each step carefully and end up with the right answer (unless I did math wrong or didn't have persistence!)

My goal for the next unit is to be better organized with my quizzes and other scattered papers. Right now, I have everything in my spiral notebook and the inside cover of my binder. Also, I want to start doing more things with other people in my class, that I don't typically talk to every day. I am excited for the next chapter!

~ Connections

• My desk dresser is a small, rolling 2-drawer cabinet. All my of my school-supplies is in there, and when I open the drawer, the dresser falls over! I recognized that its center of mass had been shifted, and was beyond the base of support. 
• Just like an ice-skater, I rollerblade. Whenever I spin in circles with my arms spread out, I slow down, but when they are tucked in, I spin faster!
• Lastly, I was opening my dorm room door. My hand acted as the twisting force, and my fingers the lever arm. The door knob turned and my door opened. I actually noticed the door-stop as well.

CHEERS.

Mass of a Meter Stick -- Torque Lab

Step 1 DEMO:

The meter stick was not balanced on the edge of the table and either fell, or was not actually in a balanced state, meaning that the torques of both sides of the stick were not equal. What is torque? It is the amount of force multiplied by the lever arm that ultimately creates a rotation of the system. The meter stick is the rotation in this lab.

After speculation, (the meter stick balanced at approximately 50cm) we took the meter stick and added a 100gram weight on the end. Once it was steady, the next goal was to balance the stick again, and measure the distance between the weight/(end off the table) and where the axis of rotation was. The lab asked for pictures labeling the center of gravity, the lever arm, and the force.

Step 2 PLAN: 

The equation we used to solve for the meter stick’s mass was derived from the idea that the torque on either side was equal when balanced. Because torque is force times distance, simply put, the new equation was (Fgravity)(distance) = (Fgravity)(distance). Fgravity, we learned in chapter 2, is the same term as weight, which equals (mass)(gravity).

Now: (mass)(gravity)(distance) = (mass)(gravity)(distance)

(0.1kg)(9.8)(30.5cm from table) = (x)(9.8)(19.5 from end of table to 50cm mark)

x = 0.156 kg  OR  156 grams

Percent error: (156 – 150.7) / 150.7 = 3.5% error!!

         

SUMMARY & Explanations – The method that worked…using Mr. Roo as a resource.

*Torque:  what makes an object or system rotate; (force)(lever arm)

*Lever arm:  the distance from the axis of rotation; more distance, easier to rotate

*Force:  a push or a pull on an object; Fgravity is just the weight

*Center of Mass:  where an object’s mass is in relation to the pull of gravity ¯

*Mass:  how much matter an object has

*Weight:  the force of gravity on an object’s mass

Why things are balanced: the torque is equal on either side of a rotating object/system. The bigger the lever arm, the less force is required to rotate the object. The smaller the lever arm, the more force is needed to rotate it. They’re inversely proportional.  

Here are some pictures I made from PowerPoint:

    

   CHEERS.

Torque -- Ch. 8 Resource

We've all been on a see-saw. Well, I hope so. If you haven't, they are fun but dangerous park additions that require 2 people: one on each end. Here's a picture to clear things up.

One person sits on the left end, and another on the right. But if they're masses are not equal, the lever won't be even. The website I found embedded below provides an easy example of torque and how we find it in everyday life. 

Torque = "the product of the rotational force exerted at right angles on the lever, times the distance between the point of force and the fulcrum" (dsc.discovery.com).

• (Torque = force x distance from axis)

http://dsc.discovery.com/tv-shows/mythbusters/about-this-show/physics-of-seesaws.htm

CHEERS.

Angular Momentum -- Ch. 8 Resource

This video is focusing in on how a cat lands on its feet. It is upside-down, then flips over so quickly that it lands on all fours. But how? Look and see--





The cat pulls its legs in towards its body, or axis of rotation. This causes its rotational velocity to increase, allowing for the cat to flip fast enough before landing. However, the cat's rotational inertia is less, so it is easier to [start to] rotate.

Angular momentum = Rotational Inertia x Rotational Velocity.

• RI and RV are inversely proportional: when one increases, the other decreases.

An object has less rotational velocity if the most mass is distributed furthest away from its axis of rotation. It also has more rotational inertia because it is harder to start/stop/continue spinning.

An object has more rotational velocity if the most mass is distributed closest to its axis of rotation. It also has less rotational inertia because it is easier to start/stop/continue spinning.

Hope you enjoyed,

CHEERS.