Motion and Forces Review

This set of vocabulary flashcards covers key terminology and definitions related to motion, dynamics, friction, and circular motion as presented in Chapter Two: Motion 1.

Motion

The change of position of a body with time.

Kinematics

The branch of motion which deals with the description of how objects move without regard to forces causing their motion.

Dynamics

The branch of motion that deals with why objects move, that is what causes them to move as they do.

Random Motion

The movement of objects or particles irregularly, haphazardly, or disorderly, without a preferred direction.

Brownian motion

A specific description of random motion, such as the motion of pollen grains or smoke particles suspended in a medium.

Translational Motion

The movement of rigid bodies from one point in space to another without rotating, where every part of the object follows the same path.

Rotational Motion

A type of motion in which all points in the body move in concentric circles around a line called the axis of rotation.

Oscillatory (Vibratory) Motion

Periodic motion where a body moves to and fro, reversing direction and returning regularly to its original position at regular intervals.

Relative motion

The motion of a body measured with respect to another body or a specific frame of reference.

Linear Motion

The motion of a body in a straight path or line, such as a stone falling freely from a roof top.

Origin

A reference point in a particular frame of reference used to determine the location or point in space of an object.

Bearing

The angle between the true North line drawn at a reference point and the line joining that point to another.

Distance

A scalar quantity representing the interval between two positions or how far a body has travelled; the S.I. unit is the metre $(m)$.

Displacement

A vector quantity defined as distance travelled in a specified direction.

Speed

A scalar quantity defined as the time rate of change of distance, calculated as Speed = $\frac{\text{distance}}{\text{time}}$.

Velocity

A vector quantity defined as the time rate of change of displacement, calculated as Velocity = $\frac{\text{displacement}}{\text{time}}$.

Uniform velocity

A state where a body is said to displace equal amounts in equal time intervals, keeping its time rate of change of displacement constant.

Instantaneous velocity

The velocity of an object at any specific instant of time, which can be indicated by speedometers or the gradient of the tangent to a displacement-time curve.

Acceleration

The time rate of increase in velocity, measured in S.I. units as $ms^{-2}$; calculated as $a = \frac{v - u}{t}$.

Retardation

The time rate of decrease in velocity, also known as negative acceleration or deceleration.

Contact forces

Forces that are in touch with the body to which they are applied, such as push, pull, tension, reaction, and frictional forces.

Force Fields

Forces whose sources do not require contact with the body, including gravitational, electric, and magnetic forces.

Friction

The force acting at the surface of separation between two bodies in contact that tends to oppose the motion of one over the other.

Static or limiting frictional force

The maximum frictional force that must be overcome before a body can just begin to move over another.

Kinetic or dynamic friction

The frictional force that must be overcome so that a body can move with uniform speed over another body.

Coefficient of static friction

The ratio of the frictional force $(F)$ to the normal reaction $(R)$, denoted as $\mu = \frac{F}{R}$.

Streamlining

A method of reducing friction by shaping a body so that it can move through fluids like air or water with ease.

Uniform Circular Motion

Movement of an object with a constant speed along a circular path while its direction changes continuously.

Centripetal acceleration

Acceleration directed towards the centre of a circular path, with magnitude given by $a = \frac{v^2}{r}$.

Centripetal Force

The inward force required to keep an object moving with a constant speed in a circular path, expressed as $F_c = \frac{mv^2}{r}$.

Centrifugal Force

An equal and opposite force that balances the centripetal force to keep an object moving in a circular path, in accordance with Newton's third law.

Angular Velocity

The ratio of the angle swept/turned through to the time taken, expressed as $\omega = \frac{\theta}{t}$ in radians per second $(rad\,s^{-1})$.

Radian

The angle subtended by the arc of a circle whose length is equal to the radius of the same circle, where $360^{\circ} = 2\pi\text{ radians}$.