Unit 04“Vertical Motion”

Introduction to Vertical Motion Concepts

Activity: Can a paper and a book fall at the same rate?

• This activity shows that gravity pulls all objects at the same rate, regardless of mass, shape or size.

• Even though the paper is lighter than the book, it can fall at the same rate if you crumple it up.

• By doing that you avoid air resistance, so essentially gravity is the only force on the objects.

• When they hit the ground at the same time, it shows that gravity pulls them at the same rate!

• The flat paper and the book fall at different rates, gravity pulls at the same rate, but the force of air resistance is affecting them differently.

Watch the Following Videos about Vacuums, Atmospheres, Gravity and Air

Resistance. • http://www.teachertube.com/viewVideo.php?vid

eo_id=41342&title=Hammer_and_Feather_Drop_on_Moon

• Click on video of NASA Hammer and Feather Drop

• http://dsc.discovery.com/tv-shows/mythbusters/videos/lunar-lunacy.htm

Atmosphere

• A space or place with air molecules (gas, air)– The frictional force called “AIR RESISTANCE” is

caused by air molecules.

• Places with Atmospheres have Gravity– Gravity doesn’t depend on Air Molecules.– The force of Gravity is present any time there are

two or more masses.

• Evidence: – Things fall on Earth

Vacuum

• A space or place with no atmosphere.– This means there are no air molecules (gas molecules).– Which means no air resistance.

• Vacuums have gravity.– Gravity doesn’t depend on air molecules, the force of

Gravity is always present if there are two or more masses. – Evidence?

• Objects fall on the moon – which is essentially a vacuum.

• If there was no gravity in a vacuum then the hammer and feather wouldn’t fall in the video of the astronauts on the moon.

Are the affects of gravity different in a vacuum verses an atmosphere?

• No! • Gravity pulls at the same rate, regardless of mass

shape or size.• The affects of gravity are the same in a vacuum

and an atmosphere.• In general terms – the force of gravity depends on

the mass of the planet you are on!• On that planet the affects of gravity are the same

for all objects – regardless of their mass, shape or size.

So why do objects fall at different rates on Earth (with an atmosphere) and at

the same rate on the Moon (a vacuum)• Because atmospheres have air resistance. And air

resistance applies a resistive force to all objects.• But the force of air resistance changes based on the

shape, size or density of the object.• So different shapes and sizes fall at different rates in

an atmosphere due to air resistance.

Gravity• The force of gravity exists between any two

masses (objects). • Gravity pulls on all objects at the same rate,

regardless of mass, shape or size.– This might be hard to see in the presence of air

resistance … but in a vacuum it’s clear to see.

Air Resistance• Air Resistance pushes against objects.• Air resistance makes objects fall at different

rates in an atmosphere.

Watch the videos again – this time check your understanding!

http://www.teachertube.com/viewVideo.php?video_id=41342&title=Hammer_and_Feather_Drop_on_Moon

– Click on video of NASA Hammer and Feather Drop

• http://dsc.discovery.com/tv-shows/mythbusters/videos/lunar-lunacy.htm

Can you explain it as well as Noah and Patrick?

For the following slides, identify whether the objects are falling in a

vacuum or in an atmosphere.

Atmosphere or

Vacuum?

Atmosphere or Vacuum?

Atmosphere or Vacuum?

Atmosphere or

Vacuum?

Atmosphere or Vacuum?

Atmosphere or Vacuum?

The ball is shown at each 1 second interval. Assuming only gravity acts on the ball, write in the velocity of the ball at each second.

39.2m/s

29.4m/s

19.6m/s

9.8m/s

0m/s 0m/s

-9.8m/s

-19.6m/s

-29.4m/s

-39.2m/s

-49m/s

49m/s – 9.8m/s

29.4m/s – 9.8m/s

39.2m/s – 9.8m/s

19.6m/s – 9.8m/s

9.8m/s – 9.8m/s 0m/s – 9.8m/s

-9.8m/s – 9.8m/s

-19.6m/s – 9.8m/s

-29.4m/s – 9.8m/s

-39.2m/s – 9.8m/s

49m/s