The angle subtended at the centre of a circle by an arc equal in length to the radius of the circle.

Define angular displacement .

The angle, in radians, swept out by an object as it moves around a circle, measured with respect to the centre of orbit.

To convert an angle from degrees to radians, multiply the angle in degrees by .......... .

To convert an angle from degrees to radians, multiply the angle in degrees by π/180 .

True or False? An angle of one radian is the angle subtended when the arc length equals the circumference of the circle.

False. An angle of one radian is subtended when the arc length equals the radius of the circle, not the circumference.

Angular velocity is a .......... quantity, meaning it has both a magnitude and a direction.

Angular velocity is a vector quantity, meaning it has both a magnitude and a direction.

Define centripetal acceleration .

The acceleration of an object towards the centre of a circle, when the object moves around the circle at a constant speed.

Centripetal acceleration is always directed .......... the centre of the circle.

Centripetal acceleration is always directed towards the centre of the circle.

True or False? Because its speed is constant, an object in uniform circular motion has zero acceleration.

False. Speed being constant does not mean velocity is constant — the object's direction is continuously changing, so it has a centripetal acceleration directed towards the centre.

Define centripetal force .

The resultant force towards the centre of the circle required to keep a body in uniform circular motion. It is always directed towards the centre of the body's rotation.

Why does an object moving in a circle require a resultant force to act on it?

Because it is continuously changing direction , so it is not in equilibrium, even if its speed is constant.

Is centripetal force a distinct type of force?

No. Centripetal force is not a separate force in its own right — it is the name given to whichever resultant force (for example tension, gravity or magnetic force) keeps a body moving on a circular path.

The magnetic force on a charged particle can act as a .......... force, since it always acts at 90° to the particle's velocity.

The magnetic force on a charged particle can act as a centripetal force, since it always acts at 90° to the particle's velocity.

True or False? Centripetal force is an additional force that acts alongside gravity, tension or other forces on an object moving in a circle.

False. Centripetal force is not an extra force added to the others — it is simply the name for the resultant of the existing forces (for example tension and gravity) that points towards the centre.

Define centripetal force in terms of its direction relative to motion.

A centripetal force is always directed perpendicular to an object's direction of travel, towards the centre of the circle.

In vertical circular motion, why does the tension in the string vary continuously as the object moves around the circle?

The direction of the tension changes as the object moves, while the direction of the weight stays constant, so the resultant (centripetal) force needed varies with position.

In vertical circular motion, the tension in the string is at its .......... value at the bottom of the circle.

In vertical circular motion, the tension in the string is at its maximum value at the bottom of the circle.

True or False? In vertical circular motion, an object moves fastest at the top of the circle.

False. The object moves slowest at the top of the circle, where tension is at a minimum, and fastest at the bottom, where tension is at a maximum.

International A Level (IAL)PhysicsEdexcelFlashcards4. Further Mechanics, Fields & ParticlesCircular Motion

Circular Motion (Edexcel International A Level (IAL) Physics): Flashcards

Exam code: YPH11

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FrontRadians & Angular Displacement
Define a radian.

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Cards in this collection (30)

Define a radian.
The angle subtended at the centre of a circle by an arc equal in length to the radius of the circle.
Define angular displacement.
The angle, in radians, swept out by an object as it moves around a circle, measured with respect to the centre of orbit.
What is the equation linking angular displacement, arc length and radius?
$Δ θ = \frac{s}{r}$
How many radians are equivalent to 360°?
$2 π rad \approx 6.28 rad$
To convert an angle from degrees to radians, multiply the angle in degrees by ...........
To convert an angle from degrees to radians, multiply the angle in degrees by π/180.
True or False?
An angle of one radian is the angle subtended when the arc length equals the circumference of the circle.
False.
An angle of one radian is subtended when the arc length equals the radius of the circle, not the circumference.
Define angular velocity.
The rate of change of angular displacement, given by $ω = \frac{Δ θ}{Δ t}$ It is a vector quantity, measured in rad s^-1.
How is angular speed ω related to linear speed v and radius r?
$v = ω r$
State two equations for angular speed ω in terms of the time period T and frequency f.
$ω = \frac{2 π}{T} = 2 π f$
For two objects with the same linear speed, how does angular velocity change as the radius of orbit increases?
The object further from the centre of orbit (larger r) has a smaller angular velocity, since $ω = \frac{v}{r}$
Angular velocity is a .......... quantity, meaning it has both a magnitude and a direction.
Angular velocity is a vector quantity, meaning it has both a magnitude and a direction.
True or False?
Angular frequency (ω) and frequency (f) have the same units.
False.
Angular frequency ω is measured in rad s^-1, while frequency f is measured in Hz, even though the two are related by $ω = 2 π f$
Define centripetal acceleration.
The acceleration of an object towards the centre of a circle, when the object moves around the circle at a constant speed.
State the equation for centripetal acceleration in terms of linear speed v and radius r.
$a = \frac{v^{2}}{r}$
State the equation for centripetal acceleration in terms of radius r and angular speed ω.
$a = r ω^{2}$
In deriving centripetal acceleration, what approximation is applied as the angular displacement θ tends to zero?
The small angle approximation: $\sin θ \approx θ$ (for very small angles, in radians).
Centripetal acceleration is always directed .......... the centre of the circle.
Centripetal acceleration is always directed towards the centre of the circle.
True or False?
Because its speed is constant, an object in uniform circular motion has zero acceleration.
False.
Speed being constant does not mean velocity is constant — the object's direction is continuously changing, so it has a centripetal acceleration directed towards the centre.
Define centripetal force.
The resultant force towards the centre of the circle required to keep a body in uniform circular motion. It is always directed towards the centre of the body's rotation.
Why does an object moving in a circle require a resultant force to act on it?
Because it is continuously changing direction, so it is not in equilibrium, even if its speed is constant.
In which direction do centripetal force and centripetal acceleration act, relative to each other?
In the same direction, towards the centre of the circle, following Newton's second law $F = m a$
Is centripetal force a distinct type of force?
No. Centripetal force is not a separate force in its own right — it is the name given to whichever resultant force (for example tension, gravity or magnetic force) keeps a body moving on a circular path.
The magnetic force on a charged particle can act as a .......... force, since it always acts at 90° to the particle's velocity.
The magnetic force on a charged particle can act as a centripetal force, since it always acts at 90° to the particle's velocity.
True or False?
Centripetal force is an additional force that acts alongside gravity, tension or other forces on an object moving in a circle.
False.
Centripetal force is not an extra force added to the others — it is simply the name for the resultant of the existing forces (for example tension and gravity) that points towards the centre.
Define centripetal force in terms of its direction relative to motion.
A centripetal force is always directed perpendicular to an object's direction of travel, towards the centre of the circle.
State three equivalent equations for centripetal force F.
$F = \frac{m v^{2}}{r} = m r ω^{2} = m v ω$
In vertical circular motion, why does the tension in the string vary continuously as the object moves around the circle?
The direction of the tension changes as the object moves, while the direction of the weight stays constant, so the resultant (centripetal) force needed varies with position.
What speed condition, and tension value, define the minimum speed at the top of a vertical circle?
The minimum speed occurs when the string is taut but the tension is zero (T = 0), giving $v = \sqrt{g r}$
In vertical circular motion, the tension in the string is at its .......... value at the bottom of the circle.
In vertical circular motion, the tension in the string is at its maximum value at the bottom of the circle.
True or False?
In vertical circular motion, an object moves fastest at the top of the circle.
False.
The object moves slowest at the top of the circle, where tension is at a minimum, and fastest at the bottom, where tension is at a maximum.

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