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Flashcards in Physics Class 2 Deck (26)
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1

If circumference increases, what happens to:
1) Time?
2) Speed?

Time is the same
Speed increases too

2

With uniform circular motion, is speed and velocity constant?

Speed is consttant
Velocity is not

3

Centripetal acceleration

Ac = v^2 / r

4

Centripetal Force

Fc = (mv^2)/ r

5

Forces that act perpendicular to velocity _____ the speed, but ______.

Cannot change the speed
but can change direction

6

Torque

Force's effectiveness at making an object spin/rotate

7

Torque formula

τ = rFsinθ
Units: N X m
Torque is maximized with sin90

OR (if you're able to determine the lever arm):
τ = lF
l = rsinθ

8

In static equilibrium, what is the net torque and net force?

0 because it is motionless

9

What does 'static equilibrium mean'?

Motionless, no net torque

10

Lever arm

shortest distance from the pivot to the line of action of the force

11

Fulcrum

Part that never moves

12

Work

Measures how much force contributes to the displacement of an object

W = Fdcosθ
Units: N x m --> Joules
- can be positive, negative or 0

13

When is work +, - or 0

Positive Work
0 < θ <90

Zero Work
θ = 90

Negative Work
90 < θ < 180

14

Conservative Forces

Gravity
- what goes in, comes out

15

What does work done by gravity depend on?

Initial and final height, does not matter about path taken to reach those heights

16

Power

Rate at which work is done

Formula:
P = W/t
Units: J/s --> N x m / s --> W (watts)

17

Power for a constant force parallel to a constant velocity

P = Fv

* v = d/t

18

Kinetic Energy

Ability to do work

Formula: 1/2 mv^2
Units: kg x (m/s)^2 = J

19

Total work done if no change in other forms of energy...

Wtotal = ΔKE

If work is positive = gains KE
If work is negative = loses KE
If work is 0 = speed is constant

20

Work done by gravity

Wgravity = mgh
= -ΔPE (losing PE, gaining KE)

21

Wgravity = -ΔPE (losing PE, gaining KE)

In any spontaneous process, potential energy decreases

22

When only conservative forces are doing work...

KEi + PEi = KEf + PEf

23

Conservative vs Non-Conservative forces

KEi + PEi + Wnc = KEf + PEf
Wnc = ΔE

Conservative:
- gravity, electrostatic force, spring force
- have PE associated with them
- if they're the only forces doing work, mechanical energy is conserved

Non-conservative forces:
- kinetic friction, drag
- always do negative work
- if they're doing work, mechanical energy is not conserved

24

Simple machines

Reduce the amount of force required to do something
1. Pulleys
2. Inclined Planes

25

Mechanical Advantage

Factor by which force can be reduced when using a simple machine

MA = Fresistance / Feffort
= normal / with machine > 1

Mechanical advantage > 1 because reducing amount of force by increasing displacement. Work stays the same

F = mg ---------------------> F = mgsinθ
d = h ------------------------> d = h / sinθ
W = mgh -------------------> W = mgh

26

Efficiency

Measures how much useful work was accomplished with the energy input

Efficiency (%) = Woutput / Energy input <100% (in real world, something is always lost)