Force Review. Four Fundamental Forces Nature. Gravity Electromagnetic Strong Nuclear Weak Nuclear. Common forces. Gravity – weight, attraction between masses. Friction - surfaces, air/wind resistance Elastic/Strain/Tension – deformation of shape.
Newton’s 1st Law (Inertia)
Forces in pairs.
Fa,b = -F b,a.
S Forces = ma = F1 + F2 + F3…
Fg = 250 N
2. The 5-kg box above is pushed up a 20o incline at constant speed.
a) at constant velocity, a = 0 ma = 0
He feels the same
(100 kg)(2m/s2) + (1000 N) = 1200 N
He feels heavier.
For constant force = FDt.
Non-Constant ForceForce vs. time graph. The area under the curve = impulse or Dp change in momentum.
Work = Fd cos q.
The force must be parallel to the distance moved (0o or 180o)
For varying force = area under curve on F vs. d graph.
A grenade is launched into the air and explodes into hundreds of pieces at the top of its arc. How does the total KE and total momentum compare just before and just after the explosion?
If 0° ≤ q < 90° cosq= + W is positive .
If a = 90° cosq = 0 W is 0.
If 90° < q ≤ 180° cosq is neg W is neg.
Power = rate work gets done/E transformed.The kWh is a unit of energy equivalent to1 kW of power expended for 1 h of time.Use 1000 watts for 1 hour, that's a kilowatt-hour.
Often expressed as %.