How does the mass of a projectile and its initial velocity affect how far it flies and how fast it drops?
This resource was originally published in PhysicsQuest 2020: Force & Motion.
How does the mass of a projectile and its initial velocity affect how far it flies and how fast it drops?
We’re going to look at what happens when something moves in two directions, down and out! For example, when you throw a ball, the action of throwing the ball will make it move away from you (horizontally) but gravity will also pull it down, so the ball is moving down and out.
After reading the introduction, what is your essential question or objective for this activity?
What is a projectile?
When you throw a ball or launch something from a slingshot, what path does it take? Draw it.
Do you think a projectile moving forward very fast will hit the ground sooner or later than a projectile moving forward slowly?
With your classmates, think about how you could test those ideas.
What do you think will happen? Write a hypothesis.
Tape two chopsticks to the edge of a table 3 inches apart with about 3 inches of chopstick above the table. Do the same with the second set of chopsticks on the same table edge about 6” away from the first set.
Take two rubber bands and tie them together. Do this again with another two rubber bands.
On each set of rubber bands, put a piece of masking tape over the knot so that you have a little handle.
Put the sets of rubber bands on the chopsticks to create a slingshot!
Put strips of tape 4”, 6.5”, and 9” back from the edge of the table.
Label the balls 1 through 4 from largest to smallest.
Place ball 1 at the edge of the table in one of the chopstick sling shots and ball 2 in the other. (Figure 1)
Pull the rubber bands back to the closest strip of tape and let go, launching the balls. Put a piece of tape where each of the balls hit and label it with the ball number and the distance the rubber band was pulled back. Do this at least three times, marking with tape each time. It’s always important to do repeated trials. Find the average distance traveled. Note which ball hit the ground first.
Now do the same thing, but pull the rubber band back to the second strip of tape. Again do this 3 times and find the average. Each time, note which ball hit the ground first. Repeat for third tape position.
Repeat with balls 1 & 3, 1 & 4, 2 & 3, 2 & 4, and 3 & 4. Each time, note which ball hits the ground first. Different groups can try different initial positions of the slingshot and different combinations of masses and then have a group discussion about their findings. Repeat these combinations for each tape position.
Repeat the experiment with all the balls but instead of using the sling shot just drop the balls from the same height you were shooting the balls in previous steps. Compare the times it takes the balls to hit the ground when they are dropped — just vertical direction — vs when they are slingshot having horizontal and vertical directions. Considered if the recording time you are comparing is from the moment you release the ball from the slingshot or the moment the ball leaves the table (or surface)
Draw your design below. In this experiment what do you think are the dependent variables and which are the independent variables?
How will your design help you confirm or deny your hypothesis?
What variables are present in your experiment and how are you controlling for them?
Collect your data. Record your results.
What were your results?
Did your results support your hypothesis and why or why not?
Did you get the same results every time? Why or why not?
Additional observations.
What can you say about the effect of horizontal motion on vertical motion? How does horizontal motion affect vertical motion?
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