My Jedi Science Students… USE THE FORCE! I CAN describe the types of forces and their effects on the motion of objects.

What is a force? http://www.youtube.com/watch?v=GmlMV7bA0TM

What is a force? A FORCE is a push or a pull Forces are vectors (include size and direction) Unit = NEWTON (N) All forces are exerted from one object to another

6 Types of Forces ELECTRICAL – positive and negative charges GRAVITY – all objects with mass pull on other objects NUCLEAR – holds atoms together MAGNETIC – north and south MECHANICAL – physical push or pull FRICTION – resistance to motion when sliding

Net Forces The force that an object feels when multiple forces are acting on it.

Net Forces When two forces act in the same direction you ADD them to find the net force. When two forces act in the opposite directions you SUBTRACT them to find the net force.

Balanced vs Unbalanced Forces Net force on an object is EQUAL TO ZERO Does not produce a change in motion Net force on an object is GREATER THAN ZERO Produces a change in motion

Balanced vs Unbalanced Forces

Balanced vs Unbalanced Forces

What is friction? Friction = force that opposes the motion of two surfaces that are touching Always happens in the direction opposite of the direction of motion

Friction - SLIDING Explanation – opposes the motion of sliding objects Labeled Picture   Explanation – opposes the motion of sliding objects Additional Example – sledding, brakes on a car, writing with pencil, moving heavy furniture

Friction - STATIC Labeled Picture   Explanation – frictional force on a non-moving object Additional Example – pushing a heavy box, skis sticking to snow when not moving

Friction - ROLLING Labeled Picture   Explanation – friction between wheels and a flat surface Additional Example – bikes, cars, trains, skateboard, furniture dolly, rolling suitcase

Friction - FLUID Labeled Picture   Explanation – force that opposes the motion of objects traveling in liquids or gases Additional Example – walking on a wet floor, swimming, hand out a moving car’s window

GRAVITY – What is it? Force of attraction between two objects due to their masses.

The Law of Universal Gravitation All objects in the universe ATTRACT each other through gravitational force. Gravitational force INCREASES as mass INCREASES. (more mass = more gravity) Gravitational force DECREASES as distance INCREASES. (more distance = less gravity)

Weight vs Mass WEIGHT = measure of the gravitational pull on an object Unit = Newtons Can change depending on location MASS = amount of matter in an object Unit = kilogram Stays the same everywhere