lecture3

# lecture3 - Phys 2101 Gabriela Gonzlez Physics having...

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1 Phys 2101 Gabriela González 2 Physics having predictive value! Newton’s laws: two qualitative, one quantitative: 1. If no net force, no acceleration (either at rest, or moving with constant velocity) 2. 3. Action and reaction forces are equal and opposite. a m F =

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2 3 Motion in two dimensions, with constant acceleration: F = mg ˆ j = m a a ( t ) = g ˆ j v ( t ) = v 0 gt ˆ j x ( t ) = x 0 + v 0 t 1 2 gt 2 ˆ j g v x = v 0 cos θ ; v y = v 0 cos gt x = x 0 + v 0 cos t ; y = y 0 + v 0 sin t 1 2 gt 2 4 Uniform: constant speed (angular speed = ω , linear speed=v= ω R) Circular: constant radius R, velocity vector is not constant! a = R ω 2 =v 2 /R r = x ˆ i + y ˆ j = R (cos ˆ i + sin ˆ j ) r ( t ) = R (cos ω t ˆ i + sin t ˆ j ) v ( t ) = R ( sin t ˆ i + cos t ˆ j ) a ( t ) = R 2 (cos t ˆ i + sin t ˆ j ) F = m a
3 5 Circular: velocity vector is not constant, so there’s always acceleration. A force is always needed to produce the acceleration. If the force (and acceleration) points to the center, speed is constant. If there is a tangential component of the force, the speed will change. 6 A roller-coaster car has a mass of 1200 kg when fully loaded with passengers. As the car passes over the top of a circular hill of radius 18 m, its speed is not changing. At the top of the hill, what are the (a) magnitude F N and (b) of the normal force on the car from the track if the car’s speed is 14m/s? What are (c) F N and (d) the direction if v=11 m/s?

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## This note was uploaded on 12/01/2011 for the course PHYS 2101 taught by Professor Grouptest during the Fall '07 term at LSU.

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lecture3 - Phys 2101 Gabriela Gonzlez Physics having...

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