Friction Force opposing motion ALWAYS works in opposite direction of motion –Causes objects to slow down and stop
Types of Friction Types: 1.Static: acts on objects NOT moving Holds objects in place 2.sliding friction: objects slide to produce friction Brakes, basketball shoes 3.rolling friction: objects roll; bicycle or car tires 4.fluid friction: fluids (air, water,etc.) moving over a surface 1.Aerodynamic: shapes that make lower air friction
How much friction? Depends on materials and force between objects –Rough surfaces = more or less friction? –Smooth surfaces = more or less friction? –Heavy objects = more or less friction? –Lighter objects = more or less friction?
Gravity: Tim and Moby explain Tim and Moby explain Force that pulls objects towards each other depends on the mass of and the distance between them –Accelerates objects towards Earth Law of universal gravitation: all objects have a gravitational pull on all other objects Which object has the most gravity? Why? Which object has the least gravitational pull on it? Why?
Weight vs. Mass Mass: amount of matter in an object Weight: measure of force of gravity on an object –It’s a FORCE! –Weight = mass X gravity –The mass does not change but the weight is determined by the force of gravity! –Man on the moonMan on the moon