Human Power: Doing Work
Lesson 7 of 13
Objective: SWBAT identify collect data for data for mass, distance and time and generate and explanation of energy, work and power.
Kids LOVE this activity. It is an active hands on, minds on lab. I recommend practicing how to wind up the bottles before demonstrating to the class (insert video). I made 1 set-up per group of three students. They will need to be able to stand high enough off the floor to wind the bottles 1 meter, whilst not letting the bottles touch the floor.
Be careful with kids standing on table and chairs. We don't want any casualties in the lab!
Materials for each group of three students:
- 2 liter bottle filled with water
- 30 cm length of 1.5" PVC
- Duct tape
- 1.5 meters of heavy string or rope
Tie one end of the string around the neck of the bottle and the other to the middle of the PVC pipe. Wrap tape around the string and PVC pipe to keep it from slipping. See the images below.
This lesson has been adapted from Energy Basics, by Clarkson University, Office of Educational Partnerships.
- Energy is the ability to do work (power x time)
- Work is a force acting over a distance to move an object
- Work = force X distance
- Power is how fast work is done (or the rate at which work is done)
- Power = work/time OR Power = energy / time
- Force is a push, pull or twist = mass x acceleration
To reinforce the concept of work, complete the Student Push/Pull Demo.
- Ask for two volunteers.
- Have one push against the wall and one push on a chair so that the chair moves at least 0.5 meters.
- Discuss as a class: Did either one or both of these students do any work?
- The one pushing on the chair did work; the other did not.
- “Work”requires that an object be moved.
- Did either of these expend energy?
- Yes – energy contributes to doing work, but not all energy successfully does work.
This is my procedure for set up of the experiment:
- Collect all equipment and materials necessary to conduct the activity. You will need 7 of the set ups.
- Split students into groups of 2-3 students.
- Attach one end of the rope to the bottle and the other end to the middle of the pole.
- Measure the distance of the rope from the PVC to the bottle and record it on the space given (meters, m).
Do work and collect data:
- Have each person stand on a chair and hold the pole horizontally so that the bottle is suspended. Twist the pole so the rope winds around it, lifting the bottle. Time how fast each person can wind the rope to bring the bottle all the way up to the pole.
- Record your data (in seconds).
- Repeat so that each student has 3 tries, and record each time.
- Using the given mass for your bottle, calculate Force by using: Force (N) = mass (kg) x acceleration (m/ s2 )
Mass, m = given (kg)
Acceleration due to gravity, a = 9.81 m/ s2
Use the worksheet to calculate average time for each person, work, power in Watts and horsepower (remember that 1 hp = 746 watts).
in the video below to my students reflect on how this activity helped them calculates and understand force, work, energy, and power.
- What is power?
- What does it mean if one person has a higher value for power?
- How many of you would it take to light a 60 Watt light bulb? v60 Watts ÷ Your Power (from the table) = “your name” power; 60 Watts ÷ Watts = “ “ power
- How does your person power compare to the horsepower in a car? (Use an estimated horsepower of 166.)
Using the data collected in the activity, calculate average time and apply the appropriate formulas to calculate work and power. Calculate a few of the trials in class, have students finish the calculations for homework.
- Hold up a 60 Watt light bulb and ask if anybody in the class produced enough power to light the bulb (hopefully no one actually does). Ask if they could produce more power possibly with their legs. (Give the example of the human powered bike headlights).
- Ask and/or lead a student (on the board) through a calculation of how many of themselves it would take to light the bulb, based on their power output from the activity. # of people to light 60 Watt bulb = 60 watts/power from the activity.
- (For example, if the student’s name was Nate and it took 300 of them to light the bulb, it is therefore a 300 "Natepower" bulb.)