1. C H A P T E R 4 Forces and Newton's Laws of Motion

2. 4.5 Newton's Third Law of Motion

3. 4.5 Newton's Third Law of Motion

4. 4.5 Newton's Third Law of Motion
Whenever one body exerts a force on a second body, the second body exerts an oppositely directed force of equal magnitude on the first body.

5. Examples of Newton's 3rd Law

6. Example 4
Suppose that the mass of the spacecraft in Figure 4.7 is mS = kg and that the mass of the astronaut is mA = 92 kg. In addition, assume that the astronaut exerts a force of P = +36 N on the spacecraft. Find the accelerations of the spacecraft and the astronaut.

7. Example 4
Suppose that the mass of the spacecraft in Figure 4.7 is mS = kg and that the mass of the astronaut is mA = 92 kg. In addition, assume that the astronaut exerts a force of P = +36 N on the spacecraft. Find the accelerations of the spacecraft and the astronaut.
Astronauts use a tether to stay connected to the space capsule.

8. Application of Newton's Third Law
Some rental trailers include an automatic brake-actuating mechanism.

9. 4.6 Types of Forces:
In nature there are two general types of forces, fundamental and non-fundamental.
Fundamental forces:
Gravitational force
Strong nuclear force
Weak nuclear force-----|
Electromagnetic force--!—Electroweak force
Non-fundamental forces:
Pushing, Pulling, Kicking, Grabbing, etc….
These are related to the electromagnetic force. They arise from the interactions between the electrically charged particles that comprise atoms and molecules.

10. Fundamental Forces Fundamental Force Example Particles Affected
Relative Strength
Strong nuclear
Nucleus
Nuclear 1
Electromagnetic
+, - Charges
Charged
10-2
Weak nuclear
Radioactivity
10-15
Gravitational
Your weight
All
10-38

11. Unification of Fundamental Forces

12. Newton’s Law of Universal Gravitation
Every body in the universe attracts every other body with a force that is directly proportional to the product of the masses of the bodies and inversely proportional to the square of the distance between the bodies.

13. Newton’s Law of Universal Gravitation
Every body in the universe attracts every other body with a force that is directly proportional to the product of the masses of the bodies and inversely proportional to the square of the distance between the bodies.

14. Universal Gravitational Constant

15. Universal Gravitational Constant
The proportionality constant, G is called the universal gravitational constant. Its value in the SI system of units is, G = 6.67  10-11N.m2/Kg2.

16. Universal Gravitational Constant
The proportionality constant, G is called the universal gravitational constant. Its value in the SI system of units is, G = 6.67  10-11N.m2/Kg2.
The law of gravitation is universal and very fundamental. It can be used to understand the motions of planets and moons, determine the surface gravity of planets, and the orbital motion of artificial satellites around the Earth.

17. Acceleration Due to Gravity

18. Acceleration Due to Gravity

19. Acceleration Due to Gravity

20. Acceleration Due to Gravity
Calculate g for planet Earth at sea level.

21. Weight Weight = Mass x Gravity
The weight of an object is the gravitational force that the planet exerts on the object. The weight always acts downward, toward the center of the planet.
SI Unit of Weight: : newton (N)

22. The Hubble Space Telescope

23. Example 6
The mass of the Hubble Space Telescope is kg. Determine the weight of the telescope (a) when it was resting on the earth and (b) as it is in its orbit 598 km above the earth's surface.

24. 4.8 The Normal Force
The normal force FN is one component of the force that a surface exerts on an object with which it is in contact, namely, the component that is perpendicular to the surface.

25. Normal Force Is Not Always Equal to the Weight

26. Elevator Ride
What happens to your weight during an elevator ride?

27. Apparent Weight

28. Apparent Weight