1. Gravity and Motion
Unit 8
Section 1

2. I. Gaileo Galilei
A scientist who argued that the mass of an object does not affect the time it will take to hit the ground.
He proved his argument by dropping two cannonballs of different masses off the Leaning Tower of Pisa. What do you think happened?

4. Which will hit first…. A crumpled piece of paper OR
A flat piece of paper?
Why do you think that?

5. II. Gravity and Acceleration
a. Galileo’s experiment proved that the rate of gravity never changes.
b. All objects fall to the ground at the same rate because acceleration due to gravity is the same for all objects. (Gravity pulls down on everyone and everything with the same force)
c. All objects fall toward Earth at the rate of 9.8 m/s².
d. That means every second an object falls, it’s velocity increases by 9.8 m/s.
If this is true, why does a feather take longer to fall than a pencil?

6. III. Air Resistance
One factor can affect the rate at which objects fall to the ground and that is air resistance.
Air resistance is a force that opposes the motion of objects through the air.
In other words, it’s “air friction”.
In Galileo’s experiment, since the cannonballs were both the same size and shape, they both had the same amount of air resistance acting on them. Therefore, it proved all objects experience the same amount of gravitational pull.

7. Air Resistance and Surface Area
The amount of air resistance acting on an object depends on the size, shape, and speed of the object.
Small surface area=less air resistance
large surface area=more air resistance

8. Bowling Ball vs Feathers being dropped in world’s largest vacuum
(AFTER FREE FALL)
Felix Baumgartner, highest skydive ever

9. Bowling Ball vs. Shotput
Will a 13lb bowling ball hit the ground before or after a 4lb steel ball?

10. IV. Terminal Velocity
Terminal velocity is the constant velocity of a falling object when the force of air resistance is equal and opposite in direction to the force of gravity.
This means that the upward force of air resistance is equal to the force of gravity, and the object slows down.

11. V. Free Fall
Free fall is the motion of a body when only the force of gravity is acting on the body.
In other words, free fall can only happen if no other forces other than gravity are acting on the object. So, it’s only possible in two places: in a vacuum and in space.

12. VI. Orbit Orbit is when an object travels around another object.
Two motions cause orbit:
The object is moving forward.
The object is in freefall.

13. VII. Projectile Motion
Projectile motion is the curved path that an object follows when thrown, launched, or otherwise projected near the surface of Earth.
Projectile motion depends on two things:
Horizontal motion
Vertical motion

14. Without gravity, the ball would follow the straight red line forever into space. With gravity, the ball changes speed and direction and returns to the Earth a few seconds later.

15. Riddle me this… Does the rate of gravity change? NO
What is gravity’s effect on falling objects?
All objects will fall at the same rate of 9.8m/s2 (no matter their mass)
What is the effect of air resistance on falling objects?
A force that opposes the motion of objects through the air. Greater surface area = slower to fall Smaller surface area = faster to fall