Unit 04“Vertical Motion”

“Acceleration of Falling Objects” Lab

Purpose: • Galileo fought hard to prove to people

that gravity accelerates all objects at the same rate regardless of mass, shape or size.

• Specifically he wanted people to understand that heavier objects do not always fall more quickly.

• How can we help prove Galileo correct?

Background Information:

Predictions

•Which equation can be used?

•What variable is to be calculated to help prove Galileo’s point?

•What variable(s) can be measured?

•Other important information…

•What variable(s) are known?

Background Information:

Predictions

•Which equation can be used?

Δy=Vi(Δt) + ½a(Δt)2

•What variable is to be calculated to help prove Galileo’s point?acceleration (a)

•What variable(s) can be measured?Measure the height of the window: Δy = - 12.4mMeasure the time for each object to fall with stop watches.

•Other important information… Air Resistance affects objects differently based on the shape and size of the object. In a vacuum only the force of gravity is present – all objects would fall at the same rate

because gravity accelerates all objects at the same rate regardless of mass, shape or size. .

In an atmosphere, gravity and air resistance put a force on the object, so objects fall at different rates.

•What variable(s) are known?Vi = 0m/s (objects are dropped)

gravity gravity gravity gravity gravity

air rest.

air rest.air rest.

air rest.air rest.

Procedures and Materials: 1. Each student needs a job: 5x Ball retriever, 5x Whiteboard

recorders, 5x Timer (at least).2. From the window, Ms Bucci will drop several different

objects. (Students will be outside at ground level)3. The timers will use the stop watches to time each object as

it drops.4. All times will be recorded on the whiteboards for each

object. 5. After the drops are completed the class will return to the

classroom.6. The class will analyze the time data and three times for each

object will be chosen and recorded in the data table below.7. Students will then work in five small groups to calculate the

acceleration of one object.8. These results will be shared with the class.

Data TableTrial 1Δt1 (s)

Trial 2Δt2 (s)

Trial 3Δt3 (s)

Average Time

Δtavg (s)Steel Ball

Frisbee

Wiffle BallFoam Ball

Parachute Man

Calculations Table

ShapeMass

(grams)

Average Time

Δtavg (s)Acceleration

a (m/s2)

Steel Ball

Frisbee

Wiffle BallFoam Ball

Parachute Man

Calculations Table

ShapeMass

(grams)

Average Time

Δtavg (s)Acceleration

a (m/s2)

Steel Ball Round 86

Frisbee Flat 86

Wiffle Ball

Round 25

Foam Ball Round 32

Parachute Man

“flat” 8

Discussion Questions:• What was the acceleration due to gravity on each

of the objects?

• Is the acceleration that you calculated for each object due only to gravity?

• Why is the calculated acceleration less than the acceleration due to gravity?

1. Galileo was surrounded by people who thought that heavier objects always take less time to fall than lighter objects. In fact, many people still think this! Look at the data and results obtained in class; do you have evidence to support Galileo? Using these data and results answer the question Galileo was faced with: Do heavier objects always fall more quickly than lighter objects? (A.E.S.)

1. Galileo was surrounded by people who thought that heavier objects always take less time to fall than lighter objects. In fact, many people still think this! Look at the data and results obtained in class; do you have evidence to support Galileo? Using these data and results answer the question Galileo was faced with: Do heavier objects always fall more quickly than lighter objects? (A.E.S.)• No…• Gravity accelerates ... air resistance...• For example, the ________ had a mass_______ and took

_____ seconds to fall. But the _____ had a smaller mass of ______grams, but only took ______ seconds to fall! The lighter object fell more quickly because it was ______ and had less air resistance than the ________ object.

2. People were so used to seeing objects accelerate at different rates on Earth it was hard for them to understand that gravity accelerates all objects at the same rate regardless of mass. As a class we predicted that air resistance would affect the object’s acceleration causing the overall acceleration to be less than 9.8m/s2. Look at the data and results obtained in class; do you have evidence to support your prediction? Using data and results answer the question: If gravity pulls at the same rate regardless of mass, shape or size, why does each object have a different acceleration? (A.E.S.)

2. People were so used to seeing objects accelerate at different rates on Earth it was hard for them to understand that gravity accelerates all objects at the same rate regardless of mass. As a class we predicted that air resistance would affect the object’s acceleration causing the overall acceleration to be less than 9.8m/s2. Look at the data and results obtained in class; do you have evidence to support your prediction? Using data and results answer the question: If gravity pulls at the same rate regardless of mass, shape or size, why does each object have a different acceleration? (A.E.S.)

• …because of air resistance.• Air resistance... • For example, the _________ and ________ had the same

mass of ______. But the _______is ________ and has a lot of air resistance thus a small acceleration of _________. But the _______ is _______ and has less air resistance and therefore a bigger acceleration of _________________.

3. Recall videos and demonstration done in class; do you have evidence that gravity does pull all objects at the same rate regardless of mass, shape or size? Using these pieces of evidence answer: If this experiment were done in a vacuum on Earth what would the acceleration of each object be? (A.E.S.)

3. Recall videos and demonstration done in class; do you have evidence that gravity does pull all objects at the same rate regardless of mass, shape or size? Using these pieces of evidence answer: If this experiment were done in a vacuum on Earth what would the acceleration of each object be? (A.E.S.)

• … -9.8m/s2.• Gravity accelerates... In a vacuum... • In the video on the moon, when the astronaut dropped the

hammer and feather …• (or) A vacuum was created on the show “Mythbusters”,

and when they dropped a hammer and feather ...

4. Explain some possible sources of error encountered in this lab.

4. Explain some possible sources of error encountered in this lab.

• Air resistance is a factor in this lab but it could have affected the objects differently because of different amounts of wind during each drop.

• Human reaction time is also an error. It is difficult to start and stop the timers at exactly the right moments.