1. Notes: Chapter 11.2 Gravity

2. Gravity/ Law of Universal Gravitation
All objects in universe exert gravity on each other
Formula F= G m1m d2
The force between two objects depends on their masses and the distance between them
As mass increases, so does the gravity between them
As distance increases, the gravity between them decreases

3. Gravity/ Law of Universal Gravitation
As mass increases, so does the gravity between them (direct proportion)
As distance increases, gravity decreases (inverse proportion)

4. Field forces
This is true for all field forces, such as magnetism and electricity (Coloumb’s forces)
As distance increases, field forces decrease (inverse proportion)

5. Free Fall and Weight
Free fall: objects move with only gravity (not even friction)
can only happen in vacuum (space)
Objects fall with the same acceleration due to gravity
(Earth = 9.8 m/s2, we usually round to 10.0 m/s2)
Effect of gravity on a mass is called its weight
Weight = mass x g (accel. gravity)
Weight and mass are not the same. Mass is the amount of matter, weight is how gravity affects that matter. On the Moon you have the same mass as on Earth, but weigh a different amount (gravity is different)

6. Terminal Velocity, Orbit
An object reaches a point as it falls where the effects of air resistance balance the gravity. This is called terminal velocity.
It’s not that objects will not fall anymore, it’s that they won’t fall any faster (accelerate)
Orbiting objects are in free fall (only gravity).
They also have a forward momentum, so they don’t fall back into earth right away.

7. What hits first? A bowling ball or a golf ball?
Heavier objects get pulled more by gravity, but have more inertia. The inertia and pull of gravity balance each other out.
They hit at the same time (ignoring air res.).
Why don’t we see this with a piece of paper?
Because different objects have different amounts of air resistance.

9. Projectile Motion Note: these are velocity vectors, not force vectors.
Objects have forward motion as well as downward motion.
These two forces do not affect each other. They are independent.
In fact, the speed with which it falls will increase (accelerate), while the forward velocity is constant (object in motion…)
Note: these are velocity vectors, not force vectors.

10. Projectile Motion
Notice how on just falls down, where the other goes forward as it’s falling?
Adding the forward motion did not affect when it hit.
They both hit at the same time.

11. Projectile Motion Although both forces do not affect each other, they
do both affect the motion of the object.
It will follow a curved path (parabola).
In other words how far you throw something has no effect on how long it takes to fall. It will affect where it will land, though.

12. Monkey in tree
Bullet