# unit 7 science vocab

## 10 terms

### Sliding friction

a force exerted between two surfaces sliding against each other (must be moving)

### static friction

a force exerted between two surfaces trying to slide against each other (but not yet moving)

### lubricant

a fluid used to reduce friction by creating a thin layer between the microscopic "hills and valleys of a surface"

### ball bearings

small rotating spheres that reduce friction by changing sliding motion into rolling motion

### torque

the measure of how much twisting force causes an object to rotate

### lever arm

the perpendicular distance from the axis of rotation to the line of action of the force. it is a factor used in calculating torque.

### line of action

an imaginary line in the direction of a force and passing through the point where the force is applied

### axis of rotation

a point around which an object rotates

### rotational equilibrium

a condition that occurs when all the torques applied to an object add to zero (balanced torques)

### rotational inertia

a measure of how resistive an object is to rotation. it depends on the objects mass and how the mass is distributed. its symbol is "I"