1. Forces hold the universe together
Gravity
Forces hold the universe together

2. Gravity Holds stars together Holds solar systems together
otherwise they would explode into space from the nuclear reactions
Holds solar systems together
otherwise we would drift off into the frigid emptiness
Eureka Episode 6: Gravity

3. Gravitation is a vector quantity pointing towards the Earth’s center.
We determined
ag = 9.81 m/s2
Thus Fg = ?

4. In general a gravitational field obeys Newton’s 2nd Law On Earth, acceleration is always 9.8 m/s [ ] So, for an object on Earth the force of gravity acting on an object is

5. Example
Determine for a 3500kg car.

6. Mass vs. Weight Mass is the quantity of matter in an object.
Eureka Episode 7: Weight vs. Mass
Mass is the quantity of matter in an object.
Weight is the force of gravity on an object.
Your weight can change (for example if you were on the moon), however your mass will not change … unless you cut your arm off.

7. Gravity on the Moon
On the Moon, the gravitational field strength is only about 1/6 of that on Earth, or about 1.6 N/kg [down]. Calculate the weight of a fully outfitted astronaut on the Moon, if he has a mass of 150 kg.

9. Weightlessness
Why do people in space appear to be floating? Is it because there is no gravity in outer space?
In fact, there is lots of gravity in outer space (probably 90% of what it is on Earth). If there were none, astronauts, the space shuttle, the moon and everything else would not stick around at all!!

10. Quick Lab
How Mass and Weight are Related to Earth’s Gravitational Field

11. Practice
1. Complete the Gravity problems posted on our course site. 2. Complete the following thought experiment at Explorelearning.com (Cosmic baseball)