 Mass- the amount of atoms inside an object ◦ Mass does not change!  Weight- the pull of gravity on the mass of an object ◦ Weight changes depending on the gravity of a planet

 Gravity: The attraction between 2 objects ◦ First described by Sir Isaac Newton ◦ Why is gravity important?  It’s the force that keeps us on earth  Keeps the planets from crashing into the sun

 All objects with mass have gravity ◦ That means everyone in here has their own gravitational field! ◦ Larger objects have stronger gravity  Humans=barely measureable gravitational pull

 On Earth, gravity causes all objects to fall at 9.8m/sec (32 feet/sec) ◦ All objects fall at the same rate, no matter how much mass they have  Any difference in falling speed is because of air resistance

 We can use gravity to figure out the mass of a planet ◦ We look at the size of the orbit of its moons, and the speed the moons are moving around the planet ◦ Next, we can figure out how strong the gravitational pull is between the moon and the planet  Heavier planets=faster moons  If a planet doesn’t have a moon, we can watch how it reacts when the orbit gets near to other planets