Kinetic Energy and Work

Yolanda Mc Gehee               Lincoln Park High School
                               2001 N Orchard St 
                               Chicago IL 60614
                               (312) 534-8130

Objective:

Kinetic energy can be thought of as the energy associated with the motion of an 
object and is equivalent to work.  An example of kinetic energy is a moving 
hammer doing work on a nail.  The hammer does work on the nail by driving it 
into the wall. 
 
The main objective of this Mini-teach is for students to observe kinetic energy 
in balls of the same size but of different mass.  Students are to see that 
balls with a greater mass (weight) and greater height (velocity), have more 
kinetic energy than balls with a lesser mass (weight) and a lower height  
(velocity).  They will be able to observe this by rolling balls of various 
masses down a ramp at various heights and measuring the distance the ball moves 
a block wall.  In addition, students will be able to graph the relationship 
between the distance the block wall moves versus the mass of each ball. 
 
This Mini-teach can be used for grades 5-12.
 
Materials Needed:

For each group:
(1) ramp with rails
(2) rails
(1) block wall
(3) balls (same size, different mass)
(1) meter stick
(6) blocks 
(1) balance

Strategy:

First, obtain three balls of about the same size but, of different mass.  Weigh 
the balls on a balance to determine the mass.  Record the mass in grams.  Next 
create three data tables according to the number of blocks used, (2, 4 or 6).
In the first column of the data table, list the three balls according to their 
mass starting from the least to greatest.  For the next three columns, label 
them "trial 1", "trial 2" and "trial 3".  Label the final column "average".
This is where you will record the average distance of the three trials. 

To obtain the first set of data for the first data table, stack the two blocks 
on top of each other.  Place the ramp on top of the blocks on an angle.  At the 
bottom of the ramp, place each of the rails next to each other leaving a space 
between them.  Place the block wall securely between the two rails.  Starting at 
the top of the ramp, roll the first of the three balls down the ramp.  Allow the 
ball to hit the block wall until it has used up all of its energy (until the 
ball comes to a complete stop).  Measure the distance the block has moved with a 
meter stick.  Remember to measure the distance from the end of the ramp to the 
beginning of the block wall. 

Repeat these steps two more times using the same ball at the same height. 
Perform these same steps using the two other balls at the same height.  Do this 
for each ball at each height (4 and 6 blocks).  Record the data in the data 
charts. 

Finally, use the average distances and the mass of the balls to make a graph.  
Place the average distances on the x-axis and the mass of the balls on the 
y-axis.            

Performance Assessment:

The performance assessment used in this mini-teach is breaking a piece of wood 
with your hand.  This is done by securing a piece of wood on a board holder so 
that it won't move.  Next, make a fist with your hand making sure that your 
thumb is on the outside of your fist.  Lastly, with a very constant motion, 
force and upward swing of your body, strike the middle of the board.  Surprise, 
the board breaks! 

Question:
How do you have to move your hand to do the most work in order to break the 
board? 

Answer:
In order to do the most work and thus break the board, you must hit the board
very fast and at a constant speed.  The board should also be hit on the grain of 
the wood because this is where the board is weakest.  Finally, your hand should  
hit the board from a high distance to increase the amount of kinetic energy in  
your hand.