DO NOW

1. DO NOW What is friction?

2. Friction • The force that two surfaces exert on each other when they rub against each other. • Smooth surfaces usually produce less friction than rough surfaces. • The strength of the force of friction depends on two factors: • 1. how hard the surfaces push together • 2. the types of surfaces involved.

3. Static Friction • The friction that acts on objects that are not moving.

4. Sliding Friction • Occurs when two solid surfaces slide over each other. • Can be useful (brakes use sliding friction)

5. Rolling Friction • When an object rolls across a surface.

6. Fluid Friction • Occurs when a solid object moves through a fluid. • Flying through the air and swimming.

7. DO NOW • List the 4 types of friction and give an example of each.

8. Gravity • The force that pulls objects towards each other.

9. Universal Gravitation • Gravity acts everywhere, not just on Earth • Law of Universal Gravitation: the force of gravity works between all objects in the universe. • Any two objects in the universe attract each other… no exception • Everything around you is attracted to you, but it is not as strong as the force that is attracting you to the earth.

10. Factors affecting Gravity • Two factors affect the attraction of gravity • Mass- • the measure of the amount of matter in an object. • Everything that has mass is made of matter • The more mass an object has, the greater its gravitational force • Distance- • The farther apart two objects are the smaller the gravitational force between them.

11. Weight and Mass • Mass is the measure of the amount of matter in an object • Weight is the measure of the gravitational force exerted on an object. • Weight varies with the strength of the gravitational force but mass does not. • You would have a smaller weight on the moon because the mass of the moon is 1/8 that of the Earth.

12. Gravity and Motion • On Earth gravity is a downward force that affects all objects. • Free Fall: when the only force acting on an object is gravity. • In free fall, the force of gravity is an unbalanced force, which causes an object to accelerate. • The acceleration due to gravity on Earth is 9.8m/s2

13. Air Resistance • Objects falling through air experience a type of fluid friction called air resistance. • Falling objects with a greater surface area have a greater air resistance. • Air resistance increases with velocity • The greatest velocity that a falling object reaches is known as its terminal velocity.

14. Quick Lab • With a partner take two sheets of paper and a stop watch. • Keep the first piece of paper flat and hold it parallel to the floor. • Time how long it takes for the first piece of paper to reach the ground when you drop it from eye level. • Take the second piece of paper and crumple it into a ball. • Dropping it from the same height as the first, time how long it will take for the paper to reach the ground.

15. DO NOW • What determines the air resistance?

16. Projectile Motion • An object that is thrown is known as a projectile. • Gravity affects objects in horizontal motion the same way that it affects those in free fall.

17. Projectile Motion Lab • Get into groups of 3 or 4.

18. Newton’s First Law of Motion • An object at rest will remain at rest and an object in motion will remain in motion until acted upon by an unbalanced force.

19. Inertia • Is the tendency of an object to resist a change in motion. • Depends on mass • The greater the mass of an object the greater the force required to move it, and the greater the inertia.

20. Newton’s Second Law of Motion • Acceleration depends on the object’s mass and the net force acting on the object. • Acceleration = Net Force Mass Acceleration is measured in m/s/s or m/s2

21. Changes in Force and Mass • In order to increase acceleration you must either • increase the force exerted on it or • decrease the mass of the object • In order to decrease acceleration you must either • Decrease the force exerted on the object or • increase the mass of the object

22. DO NOW • What are Newton’s First and Second Laws of Motion? Objective: State Newton’s third law of motion and explain how an object’s momentum is determined. Key Terms Momentum Law of Conservation of Momentum

23. Newton’s Third Law of Motion • If one object exerts a force on another object, then the second object exerts a force of equal strength in the opposite direction on the first object. Or • For every action there is an equal but opposite reaction.

24. Action-Reaction Pairs • When you jump your feet push on the ground, and the ground pushes back on you • When you are rowing a boat the oar pushes on the water, and the water forces the boat forward.

29. DO NOW • Take out homework

30. Momentum • The momentum of a moving object • Momentum= Mass x Velocity

31. Conservation of Momentum • In the absence of outside forces the total momentum of objects that interact does not change. • Total momentum of any group of objects remains the same, or is conserved, unless outside forces act on the objects. • Friction is an example of an outside force.

32. Collisions with two moving objects • A red ball travels at 2 m/s while a blue ball travels at 4m/s. when they bump into each other the red ball is now moving at 4m/s while the blue car is moving at 2m/s. • Momentum is conserved-the momentum of one train decreases while the momentum of the other train increases.

33. Collision with one moving object • Moving Object transfers its momentum to stationary object.

34. Two Connected Objects • Moving object connects to stationary object and then two objects move together with the same momentum.