Definitions.Formulas Energy: The ability to do work. Work: the force that is exerted times the distance over which it is exerted work (Joules) = force (Newtons) distance (metres) = Potential energy: The energy a system possesses if it is capable of doing work but is not doing work now. Potential energy is stored energy; energy waiting to be released. Kinetic energy: The energy of motion. kinetic energy (Joules) = 1 2 () [ (/)] 2 = Gravitational potential energy: Stored energy equal to an object's mass (the gravitational force exerted downward by the object) times its height above the ground () = () (/ 2 ) () = is the acceleration due to gravity at the Earth's surface = . / Elastic potential energy: the type of energy that is stored in a flexed muscle, a coiled spring and a stretched rubber band. Force: = "F" represents force (N) "m" represents mass (kg) "" represents acceleration (/ 2 ) Power: () = () () = ( ) Acceleration: = ( ) Weight: = g.

Objective In this activity, you will examine energy transfer (potential to kinetic energy) in the pull and release of a rubber band. Because the rubber band is an elastic system, you can specifically refer to the potential energy as elastic potential energy. With the release of the elastic band, the elastic potential energy is converted to kinetic energy. Through your investigation, you will examine the distance travelled by a rubber band stretched to different lengths before release.

Materials: Metre stick Rubber bands Masking tape Procedure 1) LAB SAFETY: as we are shooting rubber bands, it is important that we work safely, i.e. no rubber band is to be released unless the area to where it is being released is clear i.e. no one nearby. Also, please follow instructions carefully in terms of the distance rubber band is pulled back. 2) Mark a start line on the floor using masking tape. This is the point you will place the metre stick to release the rubber band for each trial 3) To shoot a rubber band, hook it on the front edge of the metre stick, pull the rubber band back to the 10 cm mark on the metre stick, then release 4) Measure the distance the rubber band travelled from the start line to where it landed and record data in Table 1 ** Be sure to be consistent with the placement of the rubber band on the metre stick and the angle and height with which you hold the metre stick** 5) Repeat for a total of 5 trials for the 10 cm stretch length and calculate the average for the five trials. Record all data in Table 1 6) Repeat steps 4) to 6) above this time pulling the rubber band back to the 12 cm, then 14 cm, 16 cm, 18 cm, and 20 cm mark on the metre stick; with 5 trials and averages calculated in all cases; recording data in Table 1. Lab #4

7) GRAPHING YOUR RESULTS: Create a graph using the graph paper provided. The length that the rubber band was pulled back i.e. "Stretch Length (cm)" will be represented on the -axis and "Distance Travelled (cm)" on the -axis. We will graph the averages for distance travelled by placing a dot on the graph for average distance travelled for each stretch length. Be sure to label your graph; a title and label for - and -axis. NOTE: Do not connect the dots 8) Draw a line of best fit. 9) Complete the assigned discussion and practice problems in the space provided

Table 1: Distance travelled by elastic. Record all measurements to one decimal place

Stretch Length (cm	Trial #1 Distance Travelled (cm)	Trial #2 Distance Travelled (cm)	Trial # 3 Distance Travelled (cm)	Trial #4 Distance Travelled (cm)	Trial #5 Distance Travelled (cm)	Average Distance Travelled (cm)
10
12
14
16
18
20

Discussion:

1) Based on your graph, what is the relationship between the stretch distance and the distance travelled? Explain your answer based on your graph. (Look at your results, not the internet).

2) What does this mean about the relationship between potential and kinetic energy for our system?

3) Using your graph, estimate the distance travelled if the elastic band is stretched to 30 cm? Explain your estimate.

4) Do you think that all the elastic potential energy for the rubber band (with varying stretch length) is converted entirely to kinetic energy i.e. EPE = KE? Explain. (Again, look at your results, not the internet. Think!)

Practice problems

1. A 135 g ball is thrown with a speed of 37 m/s.

a. What is its kinetic energy?

b. What is the net work done on the ball to make it reach this speed if it started from rest?

2. How much work is done by the gravitational force when a 354 kg rock falls 1.70 m?

3. You are pushing an empty shovel across a frozen pond with a horizontal force of 36 N. Assume there is no friction

a. If the shovel accelerates at 0.75 m/s 2 , what is its mass?

b. As you are pushing, snow fill up in the shovel with a mass of 55 kg. What acceleration will the force produce now?

4.A carbon molecule (m = 1.99 x 10-26 kg) has a kinetic energy of about 7.21 x10-21 J. How fast is it moving?

5. A net force of 85 N accelerates a bike from rest to 34 km/hr in 12 s.

a. What is the mass (in kg) of the bike?

b. What is the weight (in N) of the bike?

6. During class a student (let's say their height is 1.70 m tall) lifts a 1.55 kg textbook from the floor to a height of 3.45 m above the floor. What is the potential energy of the textbook relative to:

a. The floor.

b.The top of the student's head. 4 marks

c. How is the work done by the student related to the answers in part a and b?

7. In a 100 m race, a sprinter has a power output of 1.12 kW for 10.3 s. Determine the energy output during this time. Given 1 kW = 1000 W.

9. a. What is the kinetic energy of a 4.7 kg ball rolling across a floor at 8 m/s?

b. What is the kinetic energy of a 175 g tennis ball travelling 65 m/s? Given 1 g = 0.001 kg.

c. Which object would hurt more if it hit you? Explain.