1. The Fundamental Forces of Nature 3U Physics

2. The 4 Forces The 4 fundamental forces of nature are how the fundamental particles of the universe interact.

3. The 4 Forces The 4 fundamental forces of nature are how the fundamental particles of the universe interact. All other forces (e.g. friction) are macroscopic effects of these 4 forces.

4. The 4 Forces These forces are all action-at-a-distance (or non-contact forces) and are:

5. The 4 Forces These forces are all action-at-a-distance (or non-contact forces) and are: Gravity

6. The 4 Forces These forces are all action-at-a-distance (or non-contact forces) and are: Gravity Electromagnetism (Magnetism is a relativistic effect of electrical force.)

7. The 4 Forces These forces are all action-at-a-distance (or non-contact forces) and are: Gravity Electromagnetism The Weak Nuclear Force

8. The 4 Forces These forces are all action-at-a-distance (or non-contact forces) and are: Gravity Electromagnetism The Weak Nuclear Force The Strong Nuclear Force

9. Also called the strong interaction, this is the force that binds all those electrically-repelled positively-charged particles of atomic nuclei together. It is the strongest of the 4 forces but only on the scale of atomic nuclei. At larger distances, it’s unobservable.

10. The Weak Nuclear Force Also called the weak interaction, this is the force responsible for some nuclear phenomena like beta decay.

11. Electromagnetism The force that exists between all charged particles, this force is responsible for most of the observed phenomena of everyday life (the normal force, friction, etc.). Unlike the nuclear forces, it is infinite in range.

12. Gravity The weakest of the 4 forces, it is nevertheless extremely important because it is also infinite in range and exists between all particles with mass.

13. Gravity The weakest of the 4 forces, it is nevertheless extremely important because it is also infinite in range and exists between all particles with mass. And because it is always attractive, it cannot be shielded against.

14. The proportionality

15. Note that this r is measured between the centres of mass of the objects

16. The proportionality

24. The equation G was not determined until almost a century after Newton...

25. The torsion balance To determine G, Cavendish used a torsion balance, a light, rigid rod suspended by a wire with two spheres attached to the ends of the rod. When the long rod twisted, the torsion of the wire exerted a torsional force proportional to the angle of rotation of the rod.

26. Direction Note that gravity is always an attractive force. The direction of the force is on the line between the centres of mass of the masses.

27. Example Estimate the magnitude of the gravitational attraction between you and the person sitting next to you.

28. Example Estimate the magnitude of the gravitational attraction between you and the person sitting next to you.

29. Example Estimate the magnitude of the gravitational attraction between you and the person sitting next to you.

30. Example Compare this 0.0000002 N to a 60-kg person’s weight:

31. g Note that where m E is the mass of the Earth m E = 5.98 x 10 24 kg and r E is the radius of the Earth r E = 6.38 x 10 6 m

32. g This g can be determined for any mass. For example, where m Moon is the mass of the Moon and r Moon is the radius of the Moon