PHY 011 lecture 8 outline - newtons laws wrap up

What equation reps most of newtons laws and what does it mean

F =ma

On a particular object in a particular direction

A careful assessment of acceleration means pay attention to your

Choice of axes In the free body diagram

Fluid resistance

Force that a fluid (gas or liquid) exerts on a body that moves through it

The magnitude of fluid resistance depends on

Velocity

How does fluid resistance differ from friction

• in magnitude

  • Magnitude of FR depends on velocity

Fluid resistance equations (2)

• f = kv at low speed

• ( f=Dv² )at high speed, eqn 5.5 and 5.6

Ex) what equation would you use to consider a rock dropped into water?

Sum Fy = mg - f = mg - kv = m*ay

When first released, v = 0, so ay = g

As speed increases, acceleration decreases

Ex) rock dropped into water: what is the equation that shows that as speed increases, acceleration decreases

Ay = g - (k/m)v

As v increases more, the acceleration reaches zero

Since as v increases more the acceleration reaches zero, the speed approaches…

Constant terminal speed