 #  What is the net force?  Draw a free body diagram for the car. 40 N60 N.

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 What is the net force?  Draw a free body diagram for the car. 40 N60 N

A force between two surfaces that opposes motion FRICTION Science of the Oylmpics http://nbclearn.com/olympics/cuecard /47275

 What stops a ball from rolling across the room forever and ever?  The force is called FRICTION.  Friction is a force that opposes motion between two surfaces that are in contact.

 Friction occurs because the surface of any object is rough.  All surfaces are filled with microscopic hills and valleys that make them rough.  The heavier the object the more force that is exerted on the object and more friction.

Gravel Road: High Friction Ice: Low Friction

FRICTION Motion

 Which would have more friction a 2lb book or a 5lb book?  Why do objects slow down when moving?

 Static Friction ◦ Stationary  Kinetic Friction ◦ Moving

 Static friction is the friction of an object that is not moving. The object does not move because the force of static friction balances the force being applied to it.  If you were to get up and push the wall would it move? Why not?

Friction Friction cancels out the force on the object and the object does not move!

 Kinetic Friction is moving friction.  For example rolling or pushing an object produces kinetic friction.  Do you think its easier to push a chair or roll it? Which would have more friction?

FORCE OF FRICTIO N f Motion

 Two solid surfaces slide over each other  Ex: spreading sand on an icy path ◦ Brakes pads on a bicycle ◦ Sledding down a hill ◦ Falling off of the bicycle and skinning your knee.

 Friction that occurs when an object rolling across a surface  Easier to overcome than sliding friction  Ex: skates, skateboards, cars, bicycles… anything with a tire using the wheels to move freely ◦ Rolling friction acts opposite of the direction of motion

 Friction that occurs when an object moves fluid aside ◦ Easier to overcome than sliding friction ◦ can be called air resistance or drag ◦ This is why parts that must slide over each other have oil on them ◦ Fluid friction occurs between you and the air ◦ It can be reduced by streamlining

Kinetic Friction > Static Friction is always Greater than Kinetic Friction

1. The type of surface (ice, cement, etc…) 2. The mass of the object

 Friction turns work into heat energy ◦ In every energy transformation, some energy is “lost” as heat due to friction

 Gravitational Force is a force of attraction between objects ◦ ALL objects with mass exert a force of gravity on ALL other things  discovered” by Isaac Newton  Gravity on Earth has a acceleration of 9.8 meters per second squared

If the distance between the two objects increases, the gravitational force between them decreases. If the mass of either of the objects increases, the gravitational force between them increases.

 Brain Pop Gravity  What 2 factors affect how strong the force of gravity is between 2 objects?

 Gravity depends on 2 things:  MASS and DISTANCE  Family Guy Family Guy  Big Bang (2:54-3:30) Big Bang

1. Gravitational force increases as the mass of objects increases. More massive object exerts more gravity 2. Gravitational force increases as distance between 2 objects decreases. Closer together = more gravity

3 rd rule: Gravity pulls from all sides at the same rate. -why planets and stars are round.

Weight measures the gravitational force on an object’s mass. Weight changes when gravity changes Measured in newtons (N) with a scale Mass measures the amount of matter in an object Does NOT change with gravity Measured in kilograms (kg) with a triple-beam balance

 Objects fall to the ground at the same rate because the acceleration due to gravity is the same for all objects ◦ 9.8 m/s 2 on Earth

 Air resistance (fluid friction) is a force that acts to slow falling objects; results from upward force of air molecules, opposing gravity

 The greatest velocity a falling object reaches is its terminal velocity  Net force = 0 N  object stops accelerating and travels at constant speed  drag+buoyant force = gravity  http://www.youtube.com/watch?v=p0IZsfzDS4s

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