Notes on Work Power and Energy
http://www.phys.unsw.edu.au/ASISTM/workmodule.html
[pic]
Work, energy, power and force.
A good way to get a feeling for work and power is to produce some yourself. In this simple exercise you will measure how much work you do and calculate how powerful you are.
Safety
You will need some stairs that you can safely run up, preferable more than one floor. Normally, you shouldn't run on stairs. So you should
• not run up stairs if you are sick or have a medical problem
• check that your teacher says it's okay,
• have someone watching at each level to make sure there will be no-one else on the stairs
• only run up. Never run down stairs.
Measurement
Measure the total height of the stairs. If you have a long tape measure, you could use this. Alternatively, you could tie an object to a long piece of string, lower it vertically from the top of the stairs, and mark the length of the string from the floor level at the top to the floor level at the bottom. Then measure the length of the string. This measurement does not have to be very exact.
Ask another student to use the stopwatch to time how long it takes you to run up the stairs.
Measure your mass[1], using bathroom scales or choose a student who knows their mass.
Calculation
How much work did you do in running up the stairs? What does it depend on? First, think about these questions:
• How much work would you do if you ran up twice as high?
• Would you do more work if you carried a heavy object?
• Would you do less work to run up similar stairs on the moon, where the gravitational field is weaker and your weight would be less?
Let’s call the work you did W. It is given (approximately) by this equation: W = mgh m is your mass. g is the strength of the Earth’s gravitational field, which is approximately[2] 10 newtons per kilogram. h is the vertical distance you traveled.
Example. Suppose that your mass is 40 kg, that you live on the Earth (g = 10 newtons/kg) and that you ran up stairs
[pic]
Work, energy, power and force.
A good way to get a feeling for work and power is to produce some yourself. In this simple exercise you will measure how much work you do and calculate how powerful you are.
Safety
You will need some stairs that you can safely run up, preferable more than one floor. Normally, you shouldn't run on stairs. So you should
• not run up stairs if you are sick or have a medical problem
• check that your teacher says it's okay,
• have someone watching at each level to make sure there will be no-one else on the stairs
• only run up. Never run down stairs.
Measurement
Measure the total height of the stairs. If you have a long tape measure, you could use this. Alternatively, you could tie an object to a long piece of string, lower it vertically from the top of the stairs, and mark the length of the string from the floor level at the top to the floor level at the bottom. Then measure the length of the string. This measurement does not have to be very exact.
Ask another student to use the stopwatch to time how long it takes you to run up the stairs.
Measure your mass[1], using bathroom scales or choose a student who knows their mass.
Calculation
How much work did you do in running up the stairs? What does it depend on? First, think about these questions:
• How much work would you do if you ran up twice as high?
• Would you do more work if you carried a heavy object?
• Would you do less work to run up similar stairs on the moon, where the gravitational field is weaker and your weight would be less?
Let’s call the work you did W. It is given (approximately) by this equation: W = mgh m is your mass. g is the strength of the Earth’s gravitational field, which is approximately[2] 10 newtons per kilogram. h is the vertical distance you traveled.
Example. Suppose that your mass is 40 kg, that you live on the Earth (g = 10 newtons/kg) and that you ran up stairs