Forces and Motion Lab Results Example
A. Dropping Things
1. Record your observations in dropping two balls at a time. Put the mane of the ball
that hit the ground first or the word “same.
a. The results for most groups indicated that the Styrofoam balls did land
somewhat sooner than the other types of balls. Across the groups, there
was no clear order of precedence for the other three types of balls.
2. Do the crumpled paper and the flat paper hit the ground at the same time? Why?
a. No. The crumpled paper hits the ground before the flat paper.
b. Both papers have the same mass so the force down due to gravity is the
same for both papers. The reason the crumpled paper hits the ground first
is because it has less surface area and, therefore, less air resistance than
the flat sheet of paper.
3. Does the paper fall as fast as the book? Why? What happened when the paper
was placed on top of the book? Why?
a. The book falls faster than the paper.
b. Even though the two objects have the same surface area and, therefore, the
same air resistance, the book has a much greater mass than the paper so
the force due to gravity pulling the book down is much greater than that
pulling the paper down.
c. The two items fall at, essentially, the same rate.
d. Putting the book below the paper creates an artificial vacuum in which the
paper can fall. Since it is in a vacuum, the papers surface area and air
resistance are effectively zero and it accelerates at the same rate (9.8
m/sec2) as the book.
4. Did they all hit the ground at the same time? Which filter should land first, if
dropped from the same height? Which lands first? Why is one object slower than
another?
a. No.
b. One would expect the crumpled single filter to land first if dropped from the
same height as the single spread filter or the doubled spread filters. Next,
one would expect the doubled filters to land first before the single filter.
c. The items land in the order predicted.
d. For the crumpled filter, its surface area is much reduced making its air
resistance much lower than that for either of the open fiter arrangements.
The force down due to gravity is equal or even greater for the open filter(s)
but the reduced air resistance is great enough to cause the crumpled filter to
land first. For the two open filter configurations, here the air resistance is
the same for both but the force due to gravity is greater for the doubled filter
because the mass is double that of the single filter.
Conclusion to Part A:
If the masses of two items are equal, the one with the larger surface area and,
therefore, the greater air resistance will be slower when dropped from the same height
at the same time. Conversely, if the surface areas of two items are the same, the one
with the greater mass will be more greatly affected due to the force of gravity and will
fall faster when dropped from the same height at the same time. The acceleration due
to gravity on all items is the same (9.8 m/sec2). The force due to gravity may differ due
to their differing masses.
B. Level Force Meter
1. What happens to the bubble when the bottle starts to move? Why? What happens
to the bubble when the bottle slows down? Why?
a. The bubble initially moves in the same direction as that of the force applied
to the car. If the force is forward, the bubble moves forward initially. Once
the car has maintained a more or less constant motion, the bubble will return
to the middle of the level.
b. The reason the bubble moves forward intitially is that the inertia of the liquid
in the level tends to make the liquid stay in the same place as the car is
accelerated forward. As the car an the level move physically forward, the
liquid moves to the back of the level causing the bubble to move to the front
of the level. As the car (and level) attain a constant speed and their
acceleration approaches zero or becomes negative if the car slows down,
then the momentum of the liquid causes it to surge forward to the front of the
level which causes the bubble to temporarily move to the back of the level
and then, ultimately center itself.
c. The bubble moves initially to the back of the level as the car slows down.
d. Again, the cars acceleration is now toward the rear which means the force
acting on the car is toward the rear. The momentum of the liquid causes it
to continue forward toward the front of the level which causes the bubble to
go to the back of the level.
2. This is the same as question 1
3. Where is the bubble while you are pushing the car? What happens to the bubble
as soon as you let go?
a. The bubble remains in the center of the level as the car is being pushed with
a constant velocity.
b. When you let go of the car, it begins to decelerate and the force acting on
the car is toward the back of the car and level. Again, the momentum of the
liquid causes it to surge to the front of the level causing the bubble to be
forced to the back of the level, in the direction of force.
Conclusion to Part B:
Inertia will cause items with significant mass to remain in place while a force is
being applied to the object they are held within. They stand still while the object
containing them moves forward. Again, during deceleration of an object containing
items with mass, the momentum of the items with mass will cause them to continue
moving in the direction they were traveling while the object holding them slows down.
Part C – Flick Experiment
1. Which coin hits the ground first? Is this what you expected? Why did this happen?
a. Both coins hit the ground at the same time.
b. Yes
c. Both coins are being affected by gravity at the same rate. Both have the
same mass and both have the same acceleration due to gravity (9.8
m/sec2). So even though one of the coins has a velocity vector in a
horizontal direction, the acceleration due to gravity and, therefore, the force
acting on that coin in a downward direction will be the same as that acting
on the coin that is simply dropped. Their acceleration and subsequent
accrued velocities will be the same and they will hit the ground at the same
time if dropped from the same height.
Conclusion to Part C:
The affect due to gravity and the acceleration downward due to gravity is the
same for all free-falling objects irrespective of any other forces acting on them. If there
is no other force acting upward or downward on the objects, they will fall at the same
rate if dropped from the same height at the same time.