1 How things move and the forces that act on them.

2 In science, force is a push or a pull. Think of a game of bowling. The moving object - the ball, exerts a pushing force against anything it hits - the ten pins. What is a Force? Think of tugging on a rope. The person in the picture is exerting a pulling force on his end of the rope.

3 Characteristics of Forces 1. We cannot see forces. sometimes feel the effects they have on things. the balloons are affected by forces. 2. Forces can make things speed up. hit a tennis ball it speeds up.

4 3. Forces can make things slow down or stop. A parachute can make an object slow down because of air resistance. 4. Forces can make things change direction. ball changes direction by hitting it with a bat.

5 5. Forces can make things change shape. squeeze or kick a soccer ball, it will be compressed. 6. Forces can make things turn. use a wrench to loosen or tighten a nut.

6 Connection Forces with Motion Sometimes forces are obvious…….. Sometimes forces are NOT as obvious…….. …moving car crashing into a stationary tree. …Can you feel the force the ground exerts on your feet?

7 1. Balanced Forces – forces of the objects are equal in size and opposite in direction. when things are not moving. Types of Forces Example: Gravity pulls the table down, but the table is pushed up by the floor that it stands on…so the table does not move and the forces are balanced.

8 2. Unbalanced Forces – forces of the objects are NOT equal in size or direction or both. changes movement & direction. The hurdler has lost contact with the ground and has moved upwards. The earth’s pull is unbalanced. This makes him slow down and change direction, so he can come down to earth again. The seesaw is unbalanced because the forces are not equal. Types of Forces-Continued

9 3. Net Forces – sum of the forces on an object changes the speed or direction or both. Upward Force 245N + 245N = 490N Downward Force = 490N Net Force = 0N because the difference between the upward force and the downward force is equal to zero. What happens to the person on the swing? Types of Forces-Continued

10 Net Forces – Another Example The man is pushing with 100N and the woman is pushing with 100N while the care is in neutral. So what will happen to the car? What is the net force?

11 4. Gravity –force exerted by every object in the universe on every other object. –Pull of gravity is dependent on 2 things mass of the object distance between the objects Types of Forces-Continued Think what happens to ripe fruits such as apples that grow on trees. They will fall to the ground unless they are picked first.

12 5. Weight Types of Forces - Continued - measure of the force of gravity on an object. - changes depending on the amount of gravity – earth vs. moon – NOT the same as mass – Mass stays the same, there is no effect of gravity – Measured in NEWTONS (N). – measured with a spring scale

13 6. Bouyant Force –Upward force exerted by a fluid that pushes an object up –makes it seem to lose weight in a fluid. –(a fluid means a liquid or a gas). Types of Forces - Continued The buoyancy, keeps ships afloat. The buoyancy keeps swimmers on top of the water.

14 7. Magnetic Force / Electrical Force –Force between positive and negative charges Types of Forces - Continued Bar Magnets 8. Nuclear Force –Force that holds the nucleus of an atom together.

15 9. Centripetal Force –Force that moves in a circular motion –Examples: amusement park rides & satellites orbiting the earth Types of Forces - Continued

Friction Types of Forces - Continued There is friction between a car tire and the road with which it is in contact. - Friction is the resistance between two surfaces that are in contact with each other. - Without friction, you wouldn’t be able to walk, hold things, or keep your shoelaces tied. - Effects of Friction can be lessened with lubricants such as oil and grease. - Amount of Friction depends on 2 things - Kinds of surface - The force pressing the surface together - Friction generates heat, thus slowing objects down

17 Question: Would you expect more friction between an oily floor and a slick, leather shoe sole or between a rough sidewalk and the bottom of a tennis shoe?