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Forces and Friction

Forces and Friction. Forces. A push or pull on an object. Measured in the unit called Newtons (N) May cause acceleration [changes in motion]. Net Force. The sum of all forces acting on an object. When all the forces are in the same direction add them. 10 N. 6 N.

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Forces and Friction

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  1. Forces and Friction

  2. Forces • A push or pull on an object. • Measured in the unit called Newtons (N) • May cause acceleration [changes in motion]

  3. Net Force • The sum of all forces acting on an object. • When all the forces are in the same direction add them. 10 N 6 N The net force on this box is 16 N right.

  4. Net Force • When the forces are in opposite directions subtract them and take the direction of the larger force. 10 N 7N The net force on this box is 3 N right.

  5. Net Force When the net force on an object is not zero, we say that the forces on that object are unbalanced. 10 N 7N The net force on this box is 3 N right.

  6. Net Force When the net force on an object is zero, we say that the forces on that object are balanced. 10 N 10N The net force on this box is 0 N.

  7. Balanced Forces • All forces acting on an object are equal and opposite • The net force on the object equals 0 N

  8. Balanced Forces: Effect on motion There is no change in motion: • So if an object is moving, it keeps moving at the same speed in a straight line. • If an object is NOT MOVING it remains that way.

  9. Unbalanced Forces • All forces acting on an object do not add up to zero.

  10. Unbalanced Forces: Effect on motion There is a change in motion: • So if an object is moving, it speeds up, slows down or changes direction. • If an object is NOT MOVING it will start to move.

  11. Friction • Force that slows down motion. Friction opposes motion between any 2 objects in contact. • There is friction between any two surfaces in contact if there is potential that one could move. • Friction is in the direction opposite the direction of motion.

  12. Friction • There are different types of friction: • Static friction: friction between objects that aren’t moving, this force must be overcome to move an object. • Kinetic friction: Friction between 2 objects that are moving relative to each other. • Sliding friction: friction between 2 objects when one object is sliding past the other. • Kinetic rolling friction: Friction that occurs when one object is rolling over another object.

  13. Friction • Generally rolling friction is the lowest, so if you have a heavy box to move, put it on wheels. • Static friction is what you have to overcome if you start pushing a heavy object across the floor.

  14. Friction: Helpful or harmful? • Friction can be both helpful and harmful. • Friction between the wheels of a bike and the road, keep the bike from slipping all over the road, BUT • Friction between the moving parts of the bike make it go slower, BUT • Without friction the brakes would not cause the bike to stop.

  15. Friction: Helpful • Friction keeps you from slipping when you walk. (Don’t run on an icy sidewalk- low friction surfaces can be dangerous.) • Friction between your paper and pencil help you write. • Friction helps you wash the dishes with a sponge. • Friction is how brakes work.

  16. Friction: Harmful • Friction between moving parts in a car engine causes the temperature in a car engine to rise and the engine parts to wear out. • Friction slows you down (on a skateboard, bike, even running).

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