Physics Test 2 concepts (any equations to remember)

Work def

Measure of energy transfer when object is moved by applied force

Work characteristics

• scalar (no direction)

• independent of time

Work + and - values

No direction but can be + or - because of direction of applied force in relation to direction of moving object

+ force means object moves in direction of force

- force means object moves opposite of force (object slows)

Friction in relation to work

applied force of friction often does - work because it is opposite of motion

Work energy theorem

Net work done on an object by all forces is equal to the objects change in kinetic energy

Mechanical energy

Sum of objects total Potential and Kinetic energy (energy associated with movement)

Conservative vs nonconservative forces

Conservative: energy transformation that does not change total mechanical energy (Gravity, Spring, PE→KE)

Nonconservative: Force is dissipative and mechanical energy is not conserved (Friction, Tension, Normal)

Elastic potential energy def

Energy stored in elastic material due to stretch or compression

Hookes law def

Force needed to stretch or compress a spring a certain distance

Power def

Rate of energy transformation

KE ability to be + or -

Can only be + because its measuring energy due to motion and ignores direction

Momentum def

Mass in motion (vector)

Momentum relation to KE

KE = P²/2m

How are force and momentum related

In order to change an objects momentum an applied force is needed (Newton second law)

If no applied force then object moves in same direction and constant velocity

Impulse definition

change in momentum (applied force is needed)

When can conservation of momentum be applied

When Fnet = 0

One complete revolution in radians

2π

conversion from angle to radian

angle x (πrad/180)

angular position - and + vs angular displacement

Angular position has direction (need right hand rule)

Angular displacement does not have direction

Tangential velocity vs angular velocity

Tangential tells how fast object moves along circular path (m/s)

Angular velocity is just how quickly object rotates (rad/s)

Tangential velocity and acceleration magnitude as you get farther from axis of rotation

Both get larger as you get farther from center (equation shows r proportional to v and a)

Centripetal acceleration

Objects acceleration pointing towards axis of rotation

If object in circular rotation has constant velocity is there acceleration

Constantly changing direction so there is always a

centripetal acceleration would be only a if velocity is constant.

Centripetal force

Fictious force caused by centripetal acceleration that points towards center of axis

Forces that act as centripetal force

• Tension

• Gravity

• Friction

radius relation to Gravitational PE and force

as radius increases the gravitational PE and force become smaller

radius relation to orbiting velocity

Objects of smaller r or closer to surface, have greater speed

Torque def

turning effect caused by force that allows for rotation around an axis

Why do we use Fsin when calculating torque

use vector component of force that is perpendicular to axis of rotation

What part of object does gravity act on vs what we use for calculation

Gravity acts on all parts of an object but for calculations we treat weight as single point from center of gravity

Center of gravity

Point at which weight can be treated as a single force

Net gravitational torque about center of gravity

is 0

uniform gravitational field effect on Cg and Cm

They are in same spot (for problems in class we assume uniform center of gravity)

for Cm calculations what determines x

distance from same origin

Center of mass in uniform object

At its center

Center of mass in irregular object hanging

directly under point of attachment when at rest (equilibrium established)

Center of mass acceleration in relation to net force

If there is net external force than Cm accelerates

If there is zero net external force then Cm has no acceleration and moves at constant velocity

Equilibrium conditions

Translational and rotational equilibrium must be established

netF = 0 no linear a

netT = 0 no angular a

Torque relation to acceleration

Net torque gives acceleration

0 torque means constant angular velocity (0 angular acceleration)

rotation axis (baton problems) thing to remember

Not at origin but is an axis

Rotating disc KE

Translation KE is zero as Cm is stationary

Rotational KE is nonzero because particles are moving

What changes angular momentum

net external torque

Conservation of angular momentum

Can be used just like linear one

only applied for isolated system (0 net external torque)

Figure skater rotating faster explanation

Angular momentum is conserved so when pulling arms in, radius decreases and I decreases so angular velocity must increase