## Friday, January 05, 2018

### Friday Science: First Semester Physics in 20 Equations

I like physics. My son's taking high school physics and faces the AP exam at the end of the year. It occurred to me this morning that first semester high school physics really boils down to understanding the following 20 equations/concepts:

1. Know the basic units (lengths, time, mass) and their decimal forms (kilo-, centi-, milli-).

2. Know how to cancel out labels using multiplication, division, etc.

3. Know soh-cah-toa for vectors
(sin a = opposite/hypotenuse; cos a = adjacent/hypotenuse; tan = opposite/adjacent)
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The Big Five Motion Equations
4. d = vt

5. v2 = v1 + at

6. d = v1t + 1/2 at2

7. d = (v1 + v2)/2 * t

8. v22 = v12 + 2ad

(Substitute g for a and you have free fall equations.)
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Newton's Laws
9. First Law - a body in motion wants to stay in motion (so horizontal motion is constant if there is no friction).

10. Second Law - F = ma

11. Third Law - For every action there's an equal and opposite reaction: m1a1 = m2a2

12. Conservation of momentum, where p = mv (momentum = mass x velocity)

13. Impulse: F x t = mΔv (= change in momentum)

Friction Forces
14. The formula for the force to get something moving is Fstatic = mustatic * normal force. F = μn (The normal force is simply the reverse of weight, mg).

15. The formula for the frictional force of something moving is Fkinetic = mukinetic * normal force.
F = μn

Energy Equations
16. Kinetic Energy: K = 1/2 mv2

17. Potential Energy: U = mgh

18. There is a conservation of energy. If there is no friction, potential energy converts completely to kinetic and vice versa. If some is lost as friction or heat, the total is still the same.

19. Work done equals the difference between the start and end values of kinetic energy (work energy equation: W = K2 - K1

20. W = Fd (work = force x distance)