Define centre of gravity .

The centre of gravity is the point at which the weight of an object may be considered to act.

What condition determines whether an object is stable, in terms of its centre of gravity?

An object is stable when its centre of gravity lies above its base .

The wider the base of an object and the lower its centre of gravity, the more .......... the object becomes.

The wider the base of an object and the lower its centre of gravity, the more stable the object becomes.

True or False? An object's centre of gravity and centre of mass are always located at the same point.

False. They are identical only in a uniform gravitational field ; the centre of mass does not depend on the gravitational field, but the centre of gravity does.

Why does the Moon's centre of gravity lie closer to Earth than its centre of mass?

Because Earth's stronger gravitational field pulls the point at which the Moon's weight effectively acts closer to Earth, while its centre of mass (independent of gravity) remains at its geometric centre.

Define centre of mass .

The centre of mass is the point at which all the mass of an object may be considered to be concentrated; unlike centre of gravity, it does not depend on the gravitational field.

A moment is the turning effect of a force about a pivot.

When a force is applied at an angle to the pivot, what distance must be used in the moment equation?

The component of the distance that is perpendicular to the line of action of the force.

Placing a door handle far from the hinge .......... the perpendicular distance from the pivot, producing a greater moment for the same applied force.

Placing a door handle far from the hinge maximises the perpendicular distance from the pivot, producing a greater moment for the same applied force.

True or False? The distance used in the moment equation is always measured along the surface of the object, regardless of the angle of the applied force.

False. The perpendicular distance (or component) from the pivot to the line of action of the force must always be used.

A couple is a pair of forces, equal in magnitude and opposite in direction, that acts to produce rotation only .

What distance is used to calculate the moment of a couple, as opposed to a single force?

The perpendicular distance between the two forces (rather than the perpendicular distance from a pivot, used for a single force).

Why does a couple not cause an object to accelerate?

A couple produces a resultant force of zero , so by F = ma there is no linear acceleration, only rotation.

For a couple where the forces are applied at an angle (not perpendicular) to the distance between them, what must be found before calculating torque?

The component of the force that is perpendicular to the distance between the forces (e.g. F sin θ).

For a pair of forces to form a couple, they must be equal in magnitude, opposite in direction, and .......... to the distance between them.

For a pair of forces to form a couple, they must be equal in magnitude, opposite in direction, and perpendicular to the distance between them.

True or False? A couple produces a resultant force, causing the object to accelerate as well as rotate.

False. A couple produces zero resultant force , so the object rotates without any linear acceleration.

A LevelPhysicsCambridge (CIE)Flashcards4. Forces, Density & PressureTurning Effects of Forces

Turning Effects of Forces (Cambridge (CIE) A Level Physics): Flashcards

Exam code: 9702

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Define centre of gravity.

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Cards in this collection (19)

Define centre of gravity.
The centre of gravity is the point at which the weight of an object may be considered to act.
Where is the centre of gravity of a symmetrical object with uniform density located?
At its point of symmetry.
What condition determines whether an object is stable, in terms of its centre of gravity?
An object is stable when its centre of gravity lies above its base.
The wider the base of an object and the lower its centre of gravity, the more .......... the object becomes.
The wider the base of an object and the lower its centre of gravity, the more stable the object becomes.
True or False?
An object's centre of gravity and centre of mass are always located at the same point.
False.
They are identical only in a uniform gravitational field; the centre of mass does not depend on the gravitational field, but the centre of gravity does.
Why does the Moon's centre of gravity lie closer to Earth than its centre of mass?
Because Earth's stronger gravitational field pulls the point at which the Moon's weight effectively acts closer to Earth, while its centre of mass (independent of gravity) remains at its geometric centre.
Define centre of mass.
The centre of mass is the point at which all the mass of an object may be considered to be concentrated; unlike centre of gravity, it does not depend on the gravitational field.
Define moment.
A moment is the turning effect of a force about a pivot.
State the equation for the moment of a force.
$m o m e n t = F d$
where F is the force in newtons (N) and d is the perpendicular distance from the pivot in metres (m).
When a force is applied at an angle to the pivot, what distance must be used in the moment equation?
The component of the distance that is perpendicular to the line of action of the force.
Placing a door handle far from the hinge .......... the perpendicular distance from the pivot, producing a greater moment for the same applied force.
Placing a door handle far from the hinge maximises the perpendicular distance from the pivot, producing a greater moment for the same applied force.
True or False?
The distance used in the moment equation is always measured along the surface of the object, regardless of the angle of the applied force.
False.
The perpendicular distance (or component) from the pivot to the line of action of the force must always be used.
Define couple.
A couple is a pair of forces, equal in magnitude and opposite in direction, that acts to produce rotation only.
What distance is used to calculate the moment of a couple, as opposed to a single force?
The perpendicular distance between the two forces (rather than the perpendicular distance from a pivot, used for a single force).
Why does a couple not cause an object to accelerate?
A couple produces a resultant force of zero, so by F = ma there is no linear acceleration, only rotation.
Define torque.
Torque is the moment of a couple, calculated using $τ = F d$ , where F is one of the forces (N) and d is the perpendicular distance between them (m).
For a couple where the forces are applied at an angle (not perpendicular) to the distance between them, what must be found before calculating torque?
The component of the force that is perpendicular to the distance between the forces (e.g. F sin θ).
For a pair of forces to form a couple, they must be equal in magnitude, opposite in direction, and .......... to the distance between them.
For a pair of forces to form a couple, they must be equal in magnitude, opposite in direction, and perpendicular to the distance between them.
True or False?
A couple produces a resultant force, causing the object to accelerate as well as rotate.
False.
A couple produces zero resultant force, so the object rotates without any linear acceleration.

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