# Mechanics (physics)

## 19 terms

### scalar quantities

a unit with magnitude only.

### vector quantities

a physical quantity which has both magnitude and direction.

### the moment

the moment of a force about any point is defined as the force x perpendicular distance from the line of action of the force to the point.

### the law of moments

when an object is in equilibrium, the sum of the clockwise moments is equal to the sum of the anticlockwise moments about a pivot or point.

### centre of mass

the point through which a single force on the body has no turning effect.

### stable equilibrium

object returns to equilibrium i.e. obeys principle of moments.

### kinematics

the study of motion with constant acceleration.

### velocity

the rate of change of displacement with time or v=s/t.

### acceleration

the rate of increase in velocity with time or a=v/t.

### distance travelled

area under the line of a speed/time graph.

v = u + at
s = ½(u+v)/t
s = ut + ½ at²
v² = u² + 2as

### terminal velocity

the maximum speed of an object through a fluid. an object reaches terminal velocity when all the forces acting on it balance out.

### Newton's 1st law

every body continues in its state of rest, or uniform motion in a straight line unless external forces act upon it.

### Newton's 2nd law

a bodies rate of change of momentum is directly proportional to the force acting on it and takes place in the direction of the force. force=mass x acceleration.

### Newton's 3rd law

for every action there is an equal and opposite reaction.

### the Newton

the force which gives a mass of 1kg an acceleration of 1 meter per second.

### mass

the amount of matter in an object measured in kg.

### weight

the effect of gravity acting on a mass measured in Newton's.

### gravitational field strength

is given in size and direction by the force which acts on 1kg placed in the field. on earth it is 9.81 m/s^2 towards the earths centre of mass.