1. Chapter 4 Newton’s First Law of Motion The Law of Inertia

2. 4.1 Aristotle on Motion Aristotle said there are 2 types of motion: Natural motion 1. Natural motion – motion straight up and straight down; objects seek natural resting places Violent motion 2. Violent motion – imposed motion; objects are set in motion by forces

3. 4.2 Copernicus and the Moving Earth Aristotle believed the Sun revolves around the Earth because the Earth does not appear to be moving This view was accepted by society for many centuries.

4. Copernicus later put forward the theory that the Earth actually rotates around the Sun. Galileo, a contemporary of Copernicus, agreed with him based on his telescopic observations Galileo was persecuted for these views.

5. 4.3 Galileo on Motion Force – any push or pull Friction – the name given to the force that acts between materials that touch as they move past each other

6. Friction Without friction, an object would continue moving forever on a level surface. Once the object is in motion, no force is needed for the object to continue moving.

7. 4.3 Galileo on Motion Galileo believed the Earth IS in constant motion and that the Earth revolves around the Sun. He believed that once set in motion, an object will continue to move by itself and that it does not need a force to continue moving.

8. Figure 4.2 Objects rolling downhill tend to speed up (accelerate) Objects rolling uphill tend to slow down (decelerate) What about those on an even surface?

9. Inertia Naturally, the ball would keep going in the same direction. INERTIA –INERTIA – a resistance to change in the state of motion

10. Inertia Think about what happens when you suddenly stop a car. What does your body do?

11. Inertia

12. Your body continues to move in the same direction. You are RESISTING change in your state of motion: INERTIA!

13. 4.4Newton’s First Law of Motion Isaac Newton was born soon after Galileo died. In 1665, at the age of 23, Newton stated his 3 Laws of Motion which we still study today.

14. Newton’s First Law of Motion (Law of Inertia) “Every object continues in its state of rest, or of motion in a straight line at constant speed, unless it is compelled to change that state by forces exerted upon it”.

15. 4.5 Mass – A measure of inertia MASS –MASS – the amount of material present in an object The amount of INERTIA an object has is dependent on its mass.

16. Mass, Volume, and Weight Volume is the measure of space an object takes up. Weight is the measure of gravitational attraction an object has to Earth. notMass is not the same as weight!!

17. Force NEWTONSForce is measured in NEWTONS 9.8 Newtons (N) of force = 1 kilogram or, 1 kg = 9.8 N (on the planet Earth) Remember, gravity is a downward FORCE!

18. Example What is the weight (in Newtons) of a 10 kg bowling ball? Answer: 10 kg X 9.8 N/1 kg = 98 N

19. 4.6 Net Force Definition: The combination of all the forces that act on an object is the NET FORCE. (Figure 4.10 page 51)

20. 4.7 Equilibrium – When Net Force Equals Zero A book is laying on the table What forces are acting on the book?

21. 4.7 Equilibrium – When Net Force Equals Zero Support Force (Normal Force) – the force that balances the force of an object on the surface –(the table’s force pushing back on the book) –Normal force is equal to the weight of the book

22. 4.7 Equilibrium – When Net Force Equals Zero When an object is at rest, with the net force on it being zero, we say it is in a state of EQUILIBRIUM

23. Ch. 4 Vocabulary EQUILIBRIUM FORCE FRICTION INERTIA LAW OF INERTIA WEIGHT NEWTON’S 1 ST LAW NET FORCE KILOGRAM MASS SUPPORT FORCE NEWTON