Types of Forces & Newton’s Third Law of Motion

1. Types of Forces &Newton’s Third Law of Motion

2. Gravity • Many types of forces act on objects. • Gravity is an attractive force between all objects that have mass.

3. Gravity The ball does not travel in a straight line because of the unbalanced force of gravity acting on it.

4. The Law of Universal Gravitation • The Law of Universal Gravitation states that all objects with mass are attracted to each other. • The magnitude of attraction depends on the mass of each object and the distance between them.

5. The Law of Universal Gravitation • The gravitational force becomes stronger as either or both objects increase in mass. • The gravitational force becomes weaker as the distance between the objects increases.

6. Friction • Friction is a force that opposes the movement between two surfaces in contact. • A book pushed across a table slows down because of friction. • Friction is an unbalanced force acting on the book to slow it down.

7. Friction • Without friction, you could not walk, drive, skate, etc. • Sometimes we want to INCREASE it. (cleats, surfboard wax)

8. Friction • Friction is the force between two surfaces in contact that keeps them from sliding. • When a force is applied to a heavy box, and the box doesn’t move… • The forces are balanced, the force pushing the box equals the force of friction pushing in the opposite direction.

9. Sliding Friction • When the force pushing on the box is larger than the friction force, the box begins to slide. • The frictional force that acts on the sliding box is called sliding friction. motion

10. Sliding Friction • The book pushed across the table slows down because of sliding friction. • Without sliding friction, the book would continue moving without a force being applied.

11. Sliding Friction • Usually friction is present and an unbalancing force must be applied to keep an object moving. • When friction is greatly reduced, objects move with nearly constant velocity without an applied force.

12. Rolling & Fluid Friction • Rolling Friction – when an object rolls over a surface. • Fluid Friction – when an object moves through a gas OR a liquid (a fluid).

13. Elastic Forces • An elastic force occurs when a material is stretched or compressed. • A diving board exerts an upward elastic force on the diver when it is bent downward. • 2 types: tension and compression.

14. Tension Forces • A tension force is a pulling force exerted by an object when it is stretched, such as a rubber band.

15. Compression Forces • A compression force is a pushing force exerted by a material when it is squeezed or compressed.

16. Normal Forces • A normal force is the force exerted by an object that is perpendicular to the surface of the object.

17. Normal Forces • The cup is exerting a downward force on the table, caused by gravity. • The table is exerting an upward normal force on the cup, caused by compression.

18. Newton’s Third Law of Motion • Newton’s Third Law of Motion states that when one object exerts a force on a second object, the second object exerts an equal force in the opposite direction on the first object.

19. Newton’s Third Law of Motion • The forces two objects exert on each other are called force pairs. • The forces in a force pair are equal in size, and opposite in direction.

20. Newton’s Third Law of Motion • One of the forces in a force pair is called the action force and the other force is called the reaction force.

21. 2.2 Types of Forces A(n) ____ force is the force exerted by an object that is perpendicular to the surface of the object. A compression B elastic C normal D tension

22. 2.2 Types of Forces The gravitational force between two objects ____ as ____ increases. A increases; distance B decreases; mass C increases; velocity D decreases; distance

23. For every action force, there is a reaction force that is ____. A in the same direction B equal to the two objects C equal and in the opposite direction D unequal and in the direction of the object with less mass