Kinematics - California State University, Northridge

SAT Subject Physics Formula Reference

This guide is a compilation of about fifty of the most important physics formulas to know

for the SAT Subject test in physics. (Note that formulas are not given on the test.) Each

formula row contains a description of the variables or constants that make up the formula,

along with a brief explanation of the formula.

Kinematics

vave

?x

=

?t

vave = average velocity

?x = displacement

The definition of average velocity.

?t = elapsed time

vave

(vi + vf )

=

2

vave = average velocity

vi = initial velocity

vf = final velocity

a=

?v

?t

Another definition of the average velocity, which works

when a is constant.

a = acceleration

?v = change in velocity

The definition of acceleration.

?t = elapsed time

?x = displacement

1

?x = vi ?t + a(?t)2

2

vi = initial velocity

?t = elapsed time

Use this formula when you

don¡¯t have vf .

a = acceleration

?x = displacement

1

?x = vf ?t ? a(?t)2

2

vf = final velocity

?t = elapsed time

Use this formula when you

don¡¯t have vi .

a = acceleration

tutor

pg. 1

SAT Subject Physics Formula Reference

Kinematics (continued)

vf = final velocity

vf2 = vi2 + 2a?x

vi = initial velocity

a = acceleration

Use this formula when you

don¡¯t have ?t.

?x = displacement

Dynamics

F = force

F = ma

m = mass

a = acceleration

W = weight

W = mg

m = mass

g = acceleration due

to gravity

f = friction force

f = ?N

? = coefficient

of friction

N = normal force

p = momentum

p = mv

m = mass

v = velocity

tutor

Newton¡¯s Second Law. Here,

F is the net force on the mass

m.

The weight of an object with

mass m. This is really just

Newton¡¯s Second Law again.

The ¡°Physics is Fun¡± equation. Here, ? can be either

the kinetic coefficient of friction ?k or the static coefficient

of friction ?s .

The definition of momentum.

It is conserved (constant) if

there are no external forces on

a system.

pg. 2

SAT Subject Physics Formula Reference

Dynamics (continued)

?p = F ?t

?p = change

in momentum

F = applied force

F ?t is called the impulse.

?t = elapsed time

Work, Energy, and Power

W = work

W = F d cos ¦È

or

W = F! d

1

KE = mv 2

2

F = force

d = distance

¦È = angle between F

and the direction

of motion

F! = parallel force

KE = kinetic energy

m = mass

v = velocity

Work is done when a force

is applied to an object as it

moves a distance d. F! is the

component of F in the direction that the object is moved.

The definition of kinetic energy for a mass m with velocity v.

PE = potential energy

m = mass

PE = mgh

g = acceleration due

to gravity

The potential energy for a

mass m at a height h above

some reference level.

h = height

tutor

pg. 3

SAT Subject Physics Formula Reference

Work, Energy, Power (continued)

W = ?(KE)

W = work done

KE = kinetic energy

E = total energy

E = KE + PE

KE = kinetic energy

PE = potential energy

P = power

W

P =

?t

W = work

?t = elapsed time

The ¡°work-energy¡± theorem:

the work done by the net force

on an object equals the change

in kinetic energy of the object.

The definition of total (¡°mechanical¡±) energy. If there

is no friction, it is conserved

(stays constant).

Power is the amount of work

done per unit time (i.e., power

is the rate at which work is

done).

Circular Motion

ac = centripetal acceleration

v2

ac =

r

v = velocity

r = radius

Fc = centripetal force

mv

Fc =

r

2

m = mass

v = velocity

r = radius

tutor

The ¡°centripetal¡± acceleration

for an object moving around

in a circle of radius r at velocity v.

The ¡°centripetal¡± force that is

needed to keep an object of

mass m moving around in a

circle of radius r at velocity v.

pg. 4

SAT Subject Physics Formula Reference

Circular Motion (continued)

v = velocity

2¦Ðr

v=

T

f=

r = radius

T = period

f = frequency

1

T

T = period

This formula gives the velocity v of an object moving once

around a circle of radius r in

time T (the period).

The frequency is the number

of times per second that an

object moves around a circle.

Torques and Angular Momentum

¦Ó = torque

¦Ó = rF sin ¦È

or

¦Ó = rF¡Í

r = distance (radius)

F = force

¦È = angle between F

and the lever arm

F¡Í = perpendicular force

L = angular momentum

L = mvr

m = mass

v = velocity

r = radius

tutor

Torque is a force applied at a

distance r from the axis of rotation. F¡Í = F sin ¦È is the

component of F perpendicular to the lever arm.

Angular momentum is conserved (i.e., it stays constant)

as long as there are no external torques.

pg. 5

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