Forces and Motion Gravity

I) Gravity

A) Forces Make Things Move

1) A force is a push or a pull

a) A force can make an object speed up, slow down, stop, or change direction.

b) Soccer players apply force to the ball

B) The Force of Gravity

1) Gravity is the pull force of matter on other objects 1) Gravity is the pull force of matter on other objects. (No matter how large or small)

2) Gravity is the force of Earth’s pull on us and everything toward its center

3) Gravity holds the ocean and atmosphere close to earth’s surface

4) The greater the mass of an object the greater its gravitational force

a) Two tennis balls are not pulled together since their mass is small.

b) The Moon is large enough that it’s gravity pulls on the oceans causing high and low tides

C) Mass and Gravity

1) Mass is the amount of matter in an object

2) Small objects are not massive enough to have noticeable gravitational pull on each other

a) Two bowling balls placed close to one another do not pull towards each other.

3) Objects as massive as planets and moons have noticeable gravitational pull on objects

4) The gravitational pull between two objects is equal, however the smaller one’s movement is affected more

a) Example: The sun gravity keeps the earth in orbit

5) Some planets are so massive, they can make their star wobble, but the star still keeps the planet in orbit

D) Distance and Gravity

1) The closer two objects are the stronger the gravitational pull, the farther apart two objects are the weaker the gravitational pull

2) We feel earth’s gravity instead of the sun’s because we are closer to the earth than we are to the sun,

3) As a Spacecraft travels further from earth it is affected by earth’s gravity less

But as the spacecraft travels towards Earth, Earth’s gravity pulls on it more

E) How Gravity is Measured

1) Weight is a measure of pull of gravity on an object

2) The Metric unit of measurement for force is the Newton

a) One Newton is the force needed to change the speed of 1kg (kilogram) by 1 m (meter) in 1 second

3) The mass of an object stays the same no matter where it is, however the weight can change

a) Example: on the moon you would weigh 1/6 of your earth weight