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.