Pages 350-359 Gravity

What is gravity? Gravity is a force of attraction between objects due to their mass It is a noncontact force that acts at a distance Gravity only pulls, never pushes. So it is called an attractive force. This is why all large planetary bodies are rounded. *Smaller bodies like small moons or asteroids can be lumpy because they don’t have enough mass to pull themselves into spheres.*

What determines the force of gravity? The Law of Universal Gravitation states that all objects attract each other through gravitational force that depends on the masses involved and distance between them Distance: Objects close together have a stronger attraction than objects far apart We can’t feel the sun’s gravity because it is so far away Mass: Objects with greater mass have more attraction between them Your SIN is pulling on you, but Earth’s pull is stronger

What determines the weight of an object? FW = mg or W = mg On Earth, g = 9.8 m/s2 A student has a mass of 45.4 kg (which is 100 lbs) W = 45.4 x 9.8 = 444.92 N On the moon, g = 1.6 m/s2 W = 45.4 x 1.6 = 72.64 N On Jupiter, 24.8m/s2 W = 45.4 x 24.8 = 1125.92 N

When is an object in free fall? Something is in free fall when gravity is pulling it down and no other forces are acting on it. If you toss a ball in the air, on its way down, only gravity is pulling on it, so the ball will accelerate at 9.8m/s2 A basketball’s mass is 0.62 kg. It free falls to the floor after Sam makes a shot. F = ma = 0.62 x 9.8 = 6.1 N It will hit the floor with a force of 6.1 N.

Orbits An orbit is an elliptical path that one object takes around another object. Result of the speed of the orbiting body and the gravitational pull between two objects. Escape velocity: the speed needed to escape a planet’s gravity If the object is not projected (pushed) straight. Speeds lower than the escape velocity result in orbital motion.

Misconceptions about falling objects https://www.youtube.com/watch?v=_mCC-68LyZM