1. Unit 2 Chapter 7 Forces Lesson 3 Newton’s Laws of Motion

2. Objectives SW state Newton’s first law of motion. SW state Newton’s second law of motion. SW state Newton’s third law of motion.

3. GLEs 17 Describe and demonstrate that friction is a force that acts whenever two surfaces or objects move past one another. 19 Identify forces acting on all objects. 22 Demonstrate that an object will remain at rest or move at a constant speed and in a straight line if it is not subjected to an unbalanced force

4. Ignite! Videos Three Laws of Motion Newton’s Laws of Motion

5. My Diary Planet Horse Force “If a horse draws a stone tied to a rope, the horse (if I may say so) will be equally draw backwards towards the stone ….” Sir Isaac Newton Sir Isaac Newton

6. Vocabulary Inertia = resistance to a change in motion

7. Ignite! Videos Students will watch the videos –Three Laws of Motion –Newton’s Laws of Motion

8. What is Newton’s First Law of Motion? Newton’s first Law of Motion states that objects at rest will remain at rest unless acted upon by a nonzero force. An object moving at a constant velocity will continue moving at a constant velocity unless acted upon by a nonzero net force.

9. Inertia Newton’s first Law of Motion is also called the law of inertia. Inertia explains why you move forward in a car when a car stops suddenly. A pull on a seatbelt pulls you back. Roller coasters have safety belts for this reason.

11. Inertia Depends on Mass Some objects have more inertia than others. The greater the mass of an object, the greater the inertia and the greater the force to change the motion. Example: The larger the backpack, the harder it is to move because it has more mass, therefore more inertia.

12. Teacher Demo Forces Affect Acceleration –Place one end of a flexible ruler next to a golf ball, bending the ruler back slightly and releasing it to exert a small force on the ball. –Repeat the demonstration. Bend the ruler back further so it exerts a greater force against the ball. –Compare the forces and the motion of the ball in each trial. (The force was stronger in the second trial and the ball moved faster and farther.)

13. What is Newton’s Second Law of Motion? Newton’s Second Law of motion states that an object’s acceleration depends on its mass and on the net force acting on it. Think: –Which is harder to push? (a full shopping cart or an empty shopping cart) –Who can cause a greater acceleration on a shopping cart? (a small child or an adult)

14. Changes in Force and Mass Changing the force and the mass will change the acceleration of an object.

15. Determining Acceleration Acceleration = Net Force Mass Mass You can rearrange the formula to show how much force is applied to the object to get it to accelerate. Net Force = Mass X Acceleration Acceleration is measured in meters per second (m/s²)

16. Mass is measured in kilograms. Newton’s Second Law shows that force is measured in kilograms x meters per second per second (kg X m/s²)

17. Do the Math Every year in cities around the world, teams create cars, push them across platforms, and hope they will fly. Unfortunately, the cars always end up accelerating down into the water. Calculate: If a 100-N net force acts on a 50 –kg car, what will the acceleration of the car be?

18. Do the Math Answer: 100 N / 50 kg = 2 m/s²

19. Action – Reaction Pairs Discussion Have a student sit in a swivel chair and lift his/her feet off the floor. Ask the student to get the chair to move without touching the floor, the base of the chair, or other objects. Now use your feet to push the chair. Why is it easier to move the chair by pushing off the floor?

21. What is Newton’s Third Law of Motion? Newton’s Third Law of Motion states that 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. For every action there is a reaction! Example: If you trip, you will fall!

22. Action-Reaction Pairs Pairs of action and reaction forces are all around us. Example: You walk, then you push the ground with your feet –Swimmer pushes on the water, and the water pushes on the swimmer’s hands

23. Detecting Motion If you drop a pen on the floor, then gravity pulls the pen downward. Newton feels that the Earth pulls upward with an equal and opposite reaction force. If mass increases and force stays the same, acceleration decreases. Since Earth is such a large mass, it accelerates so small that you don’t notice it.

24. Do Action and Reaction Forces Cancel? Two equal forces acting in opposite directions on an object cancel themselves out and produce no change in motion. Action and reaction forces do not cancel each other out because they act on different objects. Example: The swimmer – action forces acts on the water while reaction forces act on the hands

25. Teacher Demo Have a student sit my rolling chair. They will toss the ball to me. Questions: –What happened when the student tossed the ball? –What made the ball move? –What made the student move?

27. Lab Activity Two students will sit on skateboards Indian style facing each other. Students will push off from each other. Students will time the skateboards as long as they are rolling. Students will measure the distance that the skateboards have moved. Students will calculate acceleration and turn in their work.

28. Objectives SW state Newton’s first law of motion. SW state Newton’s second law of motion. SW state Newton’s third law of motion.

29. GLEs 17 Describe and demonstrate that friction is a force that acts whenever two surfaces or objects move past one another. 19 Identify forces acting on all objects. 22 Demonstrate that an object will remain at rest or move at a constant speed and in a straight line if it is not subjected to an unbalanced force