Power and WorkPower and Work

Background Background InformationInformation Work (scalar)Work (scalar): Force exerted : Force exerted

over a distance. over a distance.

Unit is Joule (J)Unit is Joule (J) Power (scalar):Power (scalar): The rate at The rate at

which work is done. which work is done.

Unit is watt (W)Unit is watt (W)

Work vs. PowerWork vs. Power

Lifting an object slowly and Lifting an object slowly and quickly to the same heightquickly to the same height

Both have the same amount Both have the same amount of of workwork done done

Slowly has less Slowly has less powerpower Quickly has more Quickly has more powerpower

Power and Work LabPower and Work Lab

Objective:Objective:

To determine how much work To determine how much work and power is done in physical and power is done in physical exercises.exercises.

Hypothesis:Hypothesis:(write the questions and answer (write the questions and answer them)them)

1.1. Do you think physical Do you think physical exercises will produce exercises will produce powers greater or smaller powers greater or smaller then a light-bulb?then a light-bulb?

2.2. Do you think physical Do you think physical exercises will produce exercises will produce powers greater or smaller powers greater or smaller then a lawn mower engine?then a lawn mower engine?

Materials:Materials:

Meter stickMeter stick StopwatchStopwatch Books or other weightsBooks or other weights

(Return all materials back to (Return all materials back to the cart up front when the cart up front when finished)finished)

Procedures:Procedures:Record your own Record your own exercises!exercises! Choose an exercise that involves doing Choose an exercise that involves doing

work against the force of gravity. work against the force of gravity. Measure the distance that you exerted Measure the distance that you exerted

the force. the force. Enter your measurements in a data Enter your measurements in a data

table.table. Now, perform several repetitions (5 or Now, perform several repetitions (5 or

10) of the exercise as fast as you can 10) of the exercise as fast as you can (while being safe!). Have your lab (while being safe!). Have your lab partners count the repetitions and partners count the repetitions and measure the total time it takes. measure the total time it takes.

Repeat for three more exercises. Use Repeat for three more exercises. Use two exercises that use arm muscles, and two exercises that use arm muscles, and two exercises that use leg muscles.two exercises that use leg muscles.

Examples of ExercisesExamples of Exercises

lifting an object (arm)lifting an object (arm) raising on toes (leg)raising on toes (leg) arm curls (arm)arm curls (arm) knee bends (leg)knee bends (leg) push-ups (arm)push-ups (arm) jumping jacks (leg)jumping jacks (leg) etc. etc.

Exercise Data Table

Exercise # of Reps

Distance (m)

Time (s)

Force (N)

Work in 1 Rep. (J)

Total Work (J)

Power (w)

               

               

               

               

Conversions:Conversions:

You will need the weights in You will need the weights in Newtons for this activity, the Newtons for this activity, the force of gravity pulling down force of gravity pulling down on the object.on the object.

Book = 1.5 kgBook = 1.5 kg (1 pound = 4.45 Newtons)(1 pound = 4.45 Newtons) (F(Fgg = m = m ·· g) g)

Calculations (T-Charts)Calculations (T-Charts)

1.1. Calculate the work done in one Calculate the work done in one repetition for each exercise. repetition for each exercise. ( W ( W11 = F · d ) = F · d )

2.2. Calculate the total work done Calculate the total work done for each exercise. for each exercise. ( W ( Wtotaltotal = W = W11 × [# of reps] ) × [# of reps] )

3.3. Calculate the power done for Calculate the power done for each exercise. ( P = Weach exercise. ( P = Wtotaltotal / t ) / t )

Conclusion:Conclusion:1.1. How does the power output of your arm How does the power output of your arm

muscles compare to the power output of your muscles compare to the power output of your leg muscles? Why do you think this is? leg muscles? Why do you think this is?

2.2. How does your power output compare to the How does your power output compare to the power output of a 18 watt fluorescent bulb? power output of a 18 watt fluorescent bulb?

3.3. How does your power output compare to the How does your power output compare to the power output of a lawn mower engine? (about power output of a lawn mower engine? (about 750 watts)? 750 watts)?

4.4. Is the power output of your muscles more or Is the power output of your muscles more or less than you thought it would be? less than you thought it would be? (Hypothesis)(Hypothesis)

5.5. Did the activity that used the largest force Did the activity that used the largest force result in the largest power produced? result in the largest power produced?

6.6. Explain how a large force can result in Explain how a large force can result in relatively small power.relatively small power.

7.7. What is the relationship between work and What is the relationship between work and power?power?

8.8. What is the relationship between mass and What is the relationship between mass and weight?weight?

Make-up Data

Exercises (5 Reps for each exercise)

• Arm curls• Push ups• Jumping jacks• Knee bendsDistances• Arm curl = 43 cm• Push up = 19 cm• Jumping jack = 1.5 cm• Knee bend = 32 cm• * Covert cm to m *

Time for five reps• Arm curls = 3.25 s• Push ups = 5.13 s• Jumping jacks = 6.79 s• Knee bends = 4.83 sFind the force of gravity (weight)

in Newtons• Weight = 2.5 pounds (arm

curls)• Your weight in pounds (for

all the other exercises and ½ you weight for push ups)

• (1 pound = 4.45 Newtons)