INTRODUCTION - fill the blanks for full credits
You kick a soccer ball. Work, in Physics, measures how much _____ is transferred from a system (you) to another (the ball).
you are transferring some of your _____ potential energy to energy of _________ of the ball.
While kicking the ______, you are doing _______ on it. As a result, both the motion and the ______ energy of the ball change.
When you wind up a toy car, you transfer some of your _______ _______ energy to the spring, you are doing work on it.
As a result the spring gains _______ _______ energy which is energy stored, ready to be used again. it is now more tightly wound.
Work is done on an object only if there is a change in the mechanical energy of the object.
It could be its ________ energy, its ___________ energy or both.
When a force acts on an object and moves that object a certain _______, work is done on that object.
The work W is defined by the following equation:
W = F x D
In this equation, F represents a ______ acting on the object and D represents the_______through which the object moves as that force acts on it.
In the metric system, force is measured in ____________ (N), and distance is measured in ___________ (m).
The work is the energy transferred is expressed in the same units as energy, namely, _________ (J).
Power (P) is the rate at which work is done. It can be determined by the following equation.
P = W / t
In this equation, W represent the_______ done and t the amount of _____required to do the work.
In the metric system, the unit of power is the ________(w)
If one joule of work is done in one second, W/t has a value of 1 J/s, which is equal to 1 watt.
PURPOSE
In this experiment, you will:
PROCEDURE
1) Cut a 1.3 m length of string. Tightly tie one end of the string to the center of the wood dowel.
Secure the knot with a piece of masking tape to prevent the string from slipping.
2) Make a small loop at then other end of the string and knot it. Attach the 1-kg mass to the loop.
3) Measure a 1.00 m distance along the string from the dowel using the meter stick. Mark this distance on the string with a small strip of masking tape.
4) Hold the dowel at both ends as shown in the figure below.
5) Each of the student will wind up the string as quickly as possible. The time has to be recorded.
record the time in the table. FILL 2 FIRST COLUMNS.
| students | time (s) | work done (J) energy transfered | power (watts) | power (hp) | energy in food calorie C | energy in chocolate cookie |
| _____________ | _______ | _______ | _______ | _______ | _______ | _______ |
| _____________ | _______ | _______ | _______ | _______ | _______ | _______ |
| _____________ | _______ | _______ | _______ | _______ | _______ | _______ |
| _____________ | _______ | _______ | _______ | _______ | _______ | _______ |
ANALYSIS
1) compute the work done by your muscles on the weight. This is the energy used.
the energy transfered from you (chemical potential energy fat) to the weight. (gaining gravitational potential energy)
Work (J) = force x distance = weight (N) x distance (m) . convert kg to newtons:
weight (N) = mass (kg) x 9.8 distance in meters work in joules
FILL THIRD COLUMNS
2) compute the power produced by each student.
Power (W) = Work (J) / time (s) power in Watts.
fill the table. WHo is the most powerful ? _______________
3) convert to hp
1 hp = 746 watts fill the table.
you are as powerful as _________ (convert the hp into fraction) of a horse.
(example: 1/10 of a horse)
4) convert energy in joules (that is work done) to food calories.
1Cal = 1 food calorie= 4150 joules fill table.
5) convert to cookies.
1 cookie = about 150 Cal
6) How many cookies did you " spend" doing this exercice.