Return to Physics Index
Bowen, Sheila J. Gwendolyn Brooks Junior High
Students will be able to explain inertia.
Students will be able to identify the factors that determine inertia.
Students will be able to compare the acceleration of an object
with a net force to an object without a net force.
Students will be able to state Newton's first law of motion.
Card table, tablecloth, two china plates, heavy plastic plate, light
plastic plate, styrofoam or paper plate, plastic drinking glass, index
card, two pennies, five nickels, paper disc, small plastic disc,
three-wheeled cart or rollerskate, dot/tape time, two identical
shaped objects of different weights, 500 gram weight, distance/time
posterboard graph, average/speed posterboard graph, paste or tape.
Students should have prior knowledge of speed and acceleration
measurements and graphing.
Demonstrate inertia by snatching a tablecloth from under two china
Student teams are to complete and write up the following activities.
Each write up should include a prediction and an explanation of what
happened and why.
Activity 1 - Place a heavy plastic plate in the center of the table on
a tablecloth. Then snatch the tablecloth from under the plate.
Repeat this activity using a light plastic plate and then a styrofoam
Activity 2 - Place an index card flat on top of a plastic drinking
glass. Place a penny on the center of the card. Hold the base of
the glass with one hand. Then using the forefinger of the other
hand, flick the card forward so it moves out from under the
penny. Repeat this activity using a plastic disc and then a paper
Activity 3 - Stack 4 nickels one on top of the other. Using your
forefinger, flick another nickel sharply against the bottom coin of
the stack. Repeat this activity using the penny and then the plastic
After the activities, conduct a classroom discussion of factors of
inertia observed in each activity. Next have each student handle two
objects, identical in shape and appearance but different in weight,
to distinguish which has the greatest inertia.
Set up demonstration using a three-wheel cart or rollerskate with an
accelerometer on top. Attach the end of two tapes from the dot/tape
timer to the cart. Start the timer and give the cart an initial
push. Impress on students to observe the accelerometer. Have two
students, one for each tape, mark and cut the tape into a series of
four dot strips. Take the first strip of one of the students
and paste or tape it in the lower left corner vertically on the
distance/time posterboard graph. Then take the second strip and
paste it with its lower left corner next to the upper right corner of
the first strip. Continue pasting each successive strip until you
get to the top of the graph. Draw a line connecting the top of the
strips. With the second set of tape strips, lay them one at a time
next to each other on the horizontal axis of the average speed/time
posterboard graph. Start with the first strip to the end of the
graph. Draw a line across the top of the strips. Next tie a cord to
the cart and place the other end through a pulley at table level and
then up to a pulley on a ringstand. Attach the 500 gram weight to
the end of the cord. Once again attach two tapes from the dot/tape
timer to the cart. Repeat the demonstration releasing the weight.
Then tape the strips in the same way to each of the posterboard
The class should then compare and explain both graphs. Then discuss
inertia, its factors and Newton's first law.