Stair-Climbing Power Lab



Work Lab

Put it to Use: Work Mini Lab Problem: To investigate the scientific definition of work.

Background Information: WORK is done when a force causes an object to move in the direction of force. For work to be done, two things must occur. First, you must apply a force to an object. Second, the object must move in the same direction as the force you apply. If there is no motion, there is no work. This is very different from the way we use the word work in everyday life.

Work can be calculated with this formula: Work = Force x Distance W = F(d The units of force are Newtons and the units of distance are meters. Therefore, work is measured in Newton-Meters. These units are referred to as Joules.

Procedures:

Design an experiment to determine how much force is needed to drag a book across two different surfaces.

Stair-Climbing Power Lab

How Many Horses? It was the late 1800’s, and engineer James Watt was stumped. He’d just figured out a way to make steam engines operate much more efficiently. He wanted to start manufacturing and selling his new invention. But how could he describe how powerful these amazing engines were? Watt’s answer? Compare the power of the steam engine with something that people were very familiar with: the power of a horse. In Watt’s day, ponies (small horses) were used to pull ropes attached to platforms that lifted coal to the surface of the earth from the mine below. Watt measured how much these loads weighed (force). Then he determined how far the ponies could raise them (distance) in one minute (time). Using these measurements, he calculated how much work a pony could do in a minute – he calculated the power of a pony – pony power! At that time, the unit of work used by British scientists was the foot-pound (ft-lb). On the basis of his observations and calculations, Watt found that a pony could do 22,000 ft-lb of work a minute. Because he figured that the average horse was as powerful as 1.5 ponies, he multiplied the power of one pony (22,000 ft-lb of work per minute) by 1.5 and called it 1 horsepower (hp). In other words, 1 hp is equal to 33,000 ft-lb of work per minute, or 550 ft-lb of work per second. This means that an average horse can lift a 550-lb load a distance of 1 foot in 1 second. Horsepower can be translated into watts (W): 1 hp equals 746 W. A 350-hp engine, therefore, has the same power as a 262,500-W engine. But when numbers get as big as this, you can see that watts aren’t a convenient way of expressing the power of engines. So, the term “horsepower” stuck around. Using the word “horsepower” also probably makes drivers feel closer to the old days – when people were pioneers and mustangs were horses!!

Reading Questions:

1) Why do you think James Watt used a horse as a measure of a unit of power? _____________________________________________________________________________________________________________________________________________________

2) How did Watt decide the value of 1 horsepower? ___________________________________________________________________________ _________________________________________________________________________

3) Why is “horsepower” still a useful unit of power? __________________________________ __________________________________________________________________________

4) How many Watts make up 1 hp? ______________________________________________

5) How long did it take a horse to lift 550 lb a distance of 1 ft, according to Watt? ___________

Put it to Use: Power Up Background Information:

• You are doing WORK when you use force to cause motion in the direction of force.

• Work can be calculated mathematically.

• The formula for work is: Work = force x distance

• Time is not considered when calculating work

• Force (or weight) is measured in Newtons. Distance is measured in meters. The unit for work is a Newton-meter.

• A Newton-meter is called a Joule.

• POWER is the rate at which work is done. It is the amount to work per unit of time. • The formula for Power is: Power = work / time

• Another way to calculate it is: Power = (force x distance) / time

Objective:

1) To find out how much power you use when climbing the stars.

2) To practice calculating work and power.

Materials:

scale metric ruler stairs stopwatch

Procedure:

CAUTION: Be very careful. Make sure you hold onto the hand rail.

CAUTION: Be careful, if you are feeling overly exerted, do not continue.

Design an experiment that would help you determine the amount of power needed to climb up a staircase. Remember that your directions should include all details and be repeatable.

Observations:

1) Were the three climbing times roughly the same, or did they vary considerably?

2) Did you feel as if you exerted the same effort on each climb? Explain.

1) Was the amount of work you did for each trial the same? Why?

2) Was the amount of power you expended the same for each trial? Why or why not?

3) If you had climbed more slowly, how would the work have been affected? How would the power output have been affected? Explain you answer.

4) Compare your power output with the output of a horse by calculating your horsepower. The conversion is on the front of this lab. (Do you think you could keep up that power level for hours, like horses do?)

5) A regular car uses 180.0 horsepower of force to move. How much is this in watts?

Conclusions:

1) How does your power output in climbing the stairs compare to the power output of a 100-watt light bulb? If your power could have been harnessed and the energy converted to electricity, how many 100-watt bulbs could you have kept burning during your climb?

2) How do you calculate the amount of work done? the amount of power exerted?

3) What is the difference between work and power?

4) Two people climbed to the roof of a building. The old person walked up a gentle ramp. The young person climbed up a steep spiral staircase. Which person did more work? Explain.

5) A typical human consumes 2500 kcal of energy during a day. How much is this in joules?

(1 J = .239 calories)

6) Say you decided to run the stairs all day. How much energy in Joules would you be burning

in climbing the stairs all day in Joules? Don’t forget to convert time in seconds.

7) How many Kcal of food energy would you need to consume to do so? (4180 J = 1Kcal)

**Note: This lab was adapted from Addison-Wesley**

Work and Power Practice Problems

1. Amy uses 20N of force to push a lawn mower 10 meters. How much work does she do?

2. Joe balances a stationary coin on the tip of his finger 20cm from the top of the table. How much work is Joe doing?

3. Frank does 2400J of work in climbing a set of stairs. If he does the work in 6 seconds, what is his power output?

4. How much work is required to pull a sled if you use 60J of work in 5 seconds?

5. How much work does an elephant do while moving a circus wagon 20meters with a pulling force of 200N?

6. If it takes 5 seconds for you to do 1000J of work, what is your power output?

7. A 900N mountain climber scales a 100m cliff. How much work is done by the mountain climber?

8. A small motor does 4000J of work in 20 seconds. What is the power of the motor in watts?

9. A woman runs a kilometer using a force of 210N and a power output of 500W. How long in minutes does it take this woman to complete 1 kilometer?

10. A deflated hot-air balloon weighs a total of 8000 N. Filled with hot air, the balloon rises to a height of 1000 m. How much work is accomplished by the hot air?

11. A rope is thrown over a beam, and one end is tied to a 300 N bundle of lumber. You pull the free end of the rope 2 m with a force of 400 N to lift the lumber off the ground. How much work have you done?

12. A 150 N boy rides a 60 N bicycle a total of 200 m at a constant speed. The frictional force against the forward motion of the bicycle equals 35 N. How much work does the boy do? Explain your answer. (Hint: Remember that work is only done when the motion is in the same direction that the force is applied.)

13. A crane lifts a load of steel that weighs 9.3 _ 105 N a distance of 100 m. It takes 5 minutes to complete the task. How much work is done by the crane? How much power does the crane produce?

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Have your experiment approved before proceeding. Teacher Initials Below:

Have your experiment approved before proceeding. Teacher Initials Below:

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