Work:
Work is an energy used to generate power. It is a combination of a force and distance that must be parallel in order to generate work.
The formula for work is: work=force*distance. Make sure you know that the forces must be parallel.
For example, if you are pushing a box, and it weighs 20N and you push it 2m, this is what it would look like:
work = force*distance
work = 20N*2m
work=40 J
Work is measure in Joules.
As you can tell by the arrow, it is showing that the two forces are parallel therefore, it would produce work.
An example of forces that are not parallel, would be the same person carrying the box in this arms because the force of gravity is pulling the box down while the person is walking forward.
For work, the bigger the distance, the smaller the force and the bigger the force, the smaller the distance
w=df
w=df
Power:
Power is how fast work is done because it is a measure of work over time. It is a measure of energy that depends on how much work is done
Formula: Power=work/time
Power is measured in watts but watts isn't a random measurement, it is a measure of Joules over seconds.
Something that is used a lot today is horsepower. For example, horsepower is used in measuring the power of cars.
1 Horsepower = 746 Watts
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| I thought this was funny. Horsepower, get it? haha |
What is the power of the box being pushed by the stick figure above if she pushed it in 5 seconds?
We already know the work which is 40 J..so we can figure out the power
Power=work/time
Power=40/5
Power=8 watts
Work & Kinetic Energy Relationship:
We already know that work=force*distance and we also already know that power=work/time therefore we can figure out the relationship between work and kinetic energy.
The formula for kinetic energy is: KE=1/2mv^2
Kinetic energy is the ability for an object to do some type of motion/energy of movement.
They are similar because when you have mass and speed you can do work.
An essential question about this topic is why do airbags keep you safe, in terms of work and energy?
This would be the answer to it:
KE=1/2mv^2
ΔKE=KEfinal - KEinitial
You can go from moving to not moving regardless of how you are stopped, therefore the change in kinetic energy is the same regardless of how you are stopped.
ΔKE=work
Since the change in kinetic energy is the same regardless of what you hit, the work done on you is the same regardless of what you hit.
work = force*distance
The work is the same regardless of what is hit the airbags increase the dsitance to stop you an this reduces the force on you. Smaller force means less injury.
Conservation of Energy:
This is a simple topic, the total energy before must equal the total energy after even when something changes its movements. This topic will come in hany with both kinetic and potential energy. This also means that energy cannot be created nor destroyed. If energy is lost in many instances, it doesn't actually mean it randomly went away, it means it was transformed into other forms of energy such as heat, vibration, sound etc.
Potential Energy:
Potential energy is energy that is stored and held in a stored state that has potential of doing work. Potential energy is equal to the combination of mass, gravity, and height.
PE=mgh
this formula can directly translate to the formula for work because mg is a force and h is the distance
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| As you can see, here is the direct correlation between the two |
You can be moving and have potential energy but you can only have kinetic energy if you are not at rest. Potential energy can also be exerted when something is lifted at a certain height.
Machines:
Generally when one thinks of a machine, they assume it is a large complicated device used to assist people and make their lives easier.
The people who make this assumption are partly right. These devices don't always have to be large and complicated. They can be simple but what they do have to do is reduce the force of an object and make the job for the person easier to do.
For example, a ramp. These things seem so annoying to use but they seriously decrease the force you are doing even if they increase the distance. The work (force*distance) will always remain the same because
Other machines are: car jacks, planks, and pulleys.
Look at this example problem:
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| Property of Hannah Verity
Machines in a perfect world would have to have 100% efficiency. Because obviously this isn't a perfect world, machines are not 100 percent efficient due to energy being transformed into something else. To find out the effiency of a machine, you must use this equation:
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Difficulty:
What I found difficult about what we studied was how potential energy increases when kinetic energy decreases and vice versa. Also I idn't understand what work in = work out meant. I overcame this difficulty by doing problems for the KE and PE problem and I went to see Ms. Lawrence and I learned that work in is the work you do and work out is the work that the machine does.
Problem Solving, Skills, Effort, and Learning
In class I feel more confident in this chapter and even when I'm doing homework and blog posts I feel like I understand what is going on. I've put in effort to go to physics during my free period even if I can't go everyday. I've filled out a sheet that has all the stuff I don't understand which I've gone in to seek help for. I completed the ONQs and homework everyday.
Now I feel as if I communicate these topics in spoken and written words which I'm glad about.
In the powerhouse lab and the podcast project, I feel as if I've collaborated well with my peers and contributed in a sufficient amount.
Patience: I've definitely become more patient after last unit because even though I didn't do well on the test at all, I still know that I can get a good grade on my tests and therefore I have been patient with understanding information.
My goal for next unit: to keep doing what I'm doing now and to make any alterations to my study methods depending on how this test turns out.
Connections:
This unit was extremely useful to everyday life because I learned why trucks use ramps and why we use machines. Also, I can relate this to my own experience for when I am in the car and when I see accidents I know why and how the airbags work.
Podcast:
Here is our podcast. Enjoy!
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