Forces What causes motion?

Homework Read , Practice questions 1-3 on p351

Forces Grades Cars

Definition of a Force Forces are any push or pull on an object –Created by contact or at a distance Forces are portrayed by arrows on pictures, with the arrow pointing in the direction of the force The size of the arrow indicates the size of the force

Balanced forces Forces on an object are balanced when there is the same amount of force applied in opposite directions Balanced forces keep the object’s motion _____________

Unbalanced Forces Situation where there is more force applied in one direction than in the opposite Results in ____________

Net force The difference in size of the opposing forces is equal to the Net force on the object If the net force is zero, forces are balanced –Constant velocity If the net force is not zero, forces are not balanced –Acceleration 10 3

Freefall A specific type of motion Examples : –_____________ –_____________ (regardless of direction) To be in freefall, only the force of ______ can cause change in motion (acceleration)

Is this man in free-fall?

Answer and explanation No, because of the force of air resistance Slow speeds – air resistance can be ignored At high speeds- air resistance will have an effect

Air creates a force Each air molecule that hits the body creates an upward force The combined effort of all these molecules pushing against the body creates a force opposing gravitational pull of Earth

Terminal velocity At a high enough speeds, the press of air pushing up on the falling object = the pull of gravity The object will then no longer __________

How do the terminal velocities compare between divers?

If you dropped a spider, a penny and you off a tall building, which will land first?

Balloon Spiders

Fundamental ideas Motion is caused by forces Change of motion is caused by an imbalance of forces in opposite directions Forces come in many types, including contact, gravitational, and friction

Friction Under-acknowledged about how important it is to the normalcy of your life Force applied opposite direction of motion Amount of force depends on: –The surfaces being put together –The force used to push surfaces together