# Physics Lecture 3: Equilibrium, Torque, and Energy

## 33 terms

### Equilibrium

The condition of a system when neither its state of motion nor its internal energy state tends to change with time. It experiences neither linear acceleration nor angular acceleration

### Translational equilibrium

State where the sum of the forces acting on an object is zero, giving it no net acceleration.

### Static equilibrium

The state of an object when all forces acting on it sum to zero.

### Dynamic equilibrium

If any velocities are nonzero, but all velocities are constant

a twisting force

### t=rFsinθ

Magnitude of torque; magnitude of applied force, perpendicular distance from axis of rotation (should be 90 degrees).

### lever arm

The perpendicular distance from the axis of rotation to a line drawn along the direction of the force. t=Fl

F(up)=F(down)
F(right)=F(left)
t(cw)=t(ccw)

### Non-equilibrium equations (3 acceleration)

F(up)=F(down)±ma
F(right)=F(left)±ma
*add ma to the weaker side

### Energy

The capacity of a physical system to do work; is a scalar

### Mechanical energy

Is the kinetic and potential energy of macroscopic systems

### Kinetic energy, K=1/2mv^2

The mechanical energy that a body has by virtue of its motion.

### Potential energy

The mechanical energy that a body has by virtue of its position

### Gravitational potential energy, U=mgh

Energy due to the force of gravity near the Earth's surface. Is also depends on the height of an object.

### U=1/2k∆x^2

Elastic potential energy. Is the energy due to the resistive force applied by a deformed object.

### Law of Conservation of Energy

The fundamental principle that the total energy of an isolated system is constant despite internal changes

### Work, W=Fdcosθ

Is the transfer of energy via a force. Is a scalar and is measured in units of energy (joules). (without friction)

### Heat

Is the transfer of energy by natural flow from a warmer body to a colder body.

W=∆K+∆U+∆Ei

### Total mechanical energy

W=∆K+∆U, (no heat, no friction)

### Law of Conservation of Mechanical Energy

The sum of potential and kinetic energies of ideal energy system are constant. 0=∆K+∆U

### Conservative forces

Forces for which the work done does not depend on the path taken but only on the initial and final positions (ex. gravity)

### Nonconservative forces

Are forces that change the mechanical energy of a system when they do work.

f(k)dcosθ=∆K+∆U

### Power P=W/t

The rate of doing work.

### P=Fvcosθ

Instantaneous power

### Negative, positive

Clockwise torques are ________, CCW torques are _______.

### Zero

When force and displacement are perpendicular, the work done is _____, therefore the centripetal force does no work

### Open system

A system where energy and mass are exchanged with the surroundings

### Closed system

A system where energy is exchanged with the surroundings but mass is not.

### Isolated system

A system where neither energy nor mass is exchanged with the surroundings

### W=∆KE

Work-energy theorem

### 90º

Maximum torque when θ=____