AQA A Level Physics - Circular Motion

Comprehensive flashcards covering AQA A Level Physics Circular Motion including definitions, formulas, and conceptual explanations.

How is angular displacement ($\theta$) defined in circular motion?

The angle through which the object moves in a given time, measured in radians.

What is the formula to convert an angle from degrees to radians?

$$\frac{\text{angle in }{}^{\circ}}{180} = \frac{\text{angle in rad}}{\pi}$$

What is the formula for arc length ($s$) in terms of radius ($r$) and angular displacement ($\theta$)?

$$s = r\theta$$

What is the definition of angular speed ($\omega$)?

The rate of change of angular displacement, measured in $\text{rad\,s}^{-1}$. It is also defined by the formula $\omega = \frac{\Delta\theta}{\Delta t}$.

How is linear velocity ($v$) defined and what are its units?

The rate of change of linear displacement, measured in $\text{m\,s}^{-1}$. In circular motion, it is tangential to the path.

How do you convert angular speed from revolutions per minute (rpm) to $\text{rad\,s}^{-1}$?

Divide the value by $60$ to get $\text{rev\,s}^{-1}$, then multiply by $2\pi$.

What are the two formulas linking angular speed ($\omega$) to frequency ($f$) and time period ($T$)?

$\omega = 2\pi f$ and $\omega = \frac{2\pi}{T}$

What is the relationship between linear speed ($v$) and angular speed ($\omega$)?

$v = \omega r$ or $\omega = \frac{v}{r}$

Why is a body moving at constant speed in a circle considered to be accelerating?

Velocity is a vector and its direction is constantly changing; acceleration is defined as a change in velocity per second.

In what direction does centripetal acceleration act?

It is always directed towards the centre of the circular path.

What are the two formulas for centripetal acceleration ($a$)?

$a = \frac{v^2}{r}$ and $a = \omega^2 r$$

Why does the speed of an object in circular motion not increase due to the centripetal force?

The force is perpendicular to the displacement, so the work done is zero ($W = Fs\cos(90^{\circ}) = 0$), resulting in no increase in kinetic energy.

What are the two formulas for centripetal force ($F$)?

$F = \frac{mv^2}{r}$ and $F = m\omega^2 r$

What happens to an object’s motion if the centripetal force is removed completely?

Its linear velocity vector will stop changing and the object will move in a straight line at a tangent to the circle, obeying Newton’s 1st law.

Which forces can contribute to the resultant centripetal force?

Weight, Normal Reaction force, Tension, Friction, or Lift.

What is the direction of friction in the context of circular motion according to AQA scenarios?

Towards the centre of rotation (it is not in the opposite direction to velocity).

In vertical circular motion, where in the path is the tension in a string at its maximum?

At the bottom of the circle.

In a conical pendulum, which component of the tension provides the centripetal acceleration?

The horizontal component of the tension.

On a car traveling over a hill with radius of curvature $r$, what is the expression for the resultant centripetal force acting towards the centre?

$mg - N$, where $N$ is the normal contact force.

What is a fiducial marker?

A marker that allows timing to be made for periodic motion, used to start and stop a timer when the rotating object passes it.