A moment is the turning effect of a force, produced when a force causes an object to rotate about a pivot.

The SI unit for a moment is the ..........

The SI unit for a moment is the newton metre (N m).

Why is a door handle positioned far from the hinge?

Placing the handle far from the hinge (the pivot) maximises the perpendicular distance for a given force, producing a greater moment and making the door easier to push or pull.

Define the principle of moments .

For a system in equilibrium , the sum of clockwise moments about a point must equal the sum of anticlockwise moments about the same point.

True or False? A force produces its maximum moment when it acts parallel to the distance from the pivot.

False. A force produces its maximum moment when it acts perpendicular to the distance from the pivot; a force parallel to that distance produces no turning effect.

A couple is a pair of equal and opposite coplanar forces that acts to produce rotation only.

What three conditions must a pair of forces meet to form a couple?

Equal in magnitude Opposite in direction Perpendicular to the distance between them

The moment of a couple is equal to force multiplied by the ..........

The moment of a couple is equal to force multiplied by the perpendicular distance between the lines of action of the forces .

True or False? The moment of a couple depends on which point is chosen as the pivot.

False. Unlike the moment of a single force, the moment of a couple does not depend on a pivot.

Why can the two forces of a couple not share the same line of action?

The forces must be separated by a perpendicular distance to produce a turning effect; if they shared the same line of action there would be no couple.

Define centre of mass .

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

Where is the centre of mass located for a symmetrical object of uniform density?

At the object's point of symmetry .

How does the width of an object's base affect its stability?

A wider base gives a lower centre of mass and greater stability A narrower base gives a higher centre of mass and the object is more likely to topple

An object is stable when its centre of mass lies .......... its base.

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

In a uniform gravitational field, how does the centre of gravity compare to the centre of mass?

In a uniform gravitational field, the centre of gravity is identical to the centre of mass.

True or False? The centre of mass of an object depends on the strength of the gravitational field it is in.

False. The centre of mass does not depend on the gravitational field; it is the centre of gravity that depends on the field, since weight = mass × g .

Why does the Moon's centre of gravity shift towards Earth?

Because the centre of gravity depends on the gravitational field, and the Earth's stronger gravitational field pulls the Earth–Moon system's centre of gravity closer to Earth.

A LevelPhysicsAQAFlashcardsMechanics & MaterialsMoments

Moments (AQA A Level Physics): Flashcards

Exam code: 7408

1/20

0Still learning

Know0

FrontMoments
Define a moment.

Was this flashcard helpful?

Cards in this collection (20)

Define a moment.
A moment is the turning effect of a force, produced when a force causes an object to rotate about a pivot.
State the equation for the moment of a force, including its unit.
$Moment (N m) = Force (N) \times perpendicular distance from the pivot (m)$
The SI unit for a moment is the ..........
The SI unit for a moment is the newton metre (N m).
Why is a door handle positioned far from the hinge?
Placing the handle far from the hinge (the pivot) maximises the perpendicular distance for a given force, producing a greater moment and making the door easier to push or pull.
Define the principle of moments.
For a system in equilibrium, the sum of clockwise moments about a point must equal the sum of anticlockwise moments about the same point.
True or False?
A force produces its maximum moment when it acts parallel to the distance from the pivot.
False.
A force produces its maximum moment when it acts perpendicular to the distance from the pivot; a force parallel to that distance produces no turning effect.
A uniform metre rule is pivoted at the 50 cm mark and a weight hangs at the 80 cm mark. What is the perpendicular distance used to calculate the weight's moment?
$0.3 m$ (30 cm), the distance between the pivot at 50 cm and the weight at 80 cm.
Define a couple.
A couple is a pair of equal and opposite coplanar forces that acts to produce rotation only.
What three conditions must a pair of forces meet to form a couple?
- Equal in magnitude
- Opposite in direction
- Perpendicular to the distance between them
Why does a couple not cause an object to accelerate?
A couple produces a resultant force of zero, so by Newton's second law ( $F = m a$ ) the object does not accelerate.
The moment of a couple is equal to force multiplied by the ..........
The moment of a couple is equal to force multiplied by the perpendicular distance between the lines of action of the forces.
True or False?
The moment of a couple depends on which point is chosen as the pivot.
False.
Unlike the moment of a single force, the moment of a couple does not depend on a pivot.
Why can the two forces of a couple not share the same line of action?
The forces must be separated by a perpendicular distance to produce a turning effect; if they shared the same line of action there would be no couple.
Define centre of mass.
The centre of mass of an object is the point at which the weight of the object may be considered to act.
Where is the centre of mass located for a symmetrical object of uniform density?
At the object's point of symmetry.
How does the width of an object's base affect its stability?
- A wider base gives a lower centre of mass and greater stability
- A narrower base gives a higher centre of mass and the object is more likely to topple
An object is stable when its centre of mass lies .......... its base.
An object is stable when its centre of mass lies above its base.
In a uniform gravitational field, how does the centre of gravity compare to the centre of mass?
In a uniform gravitational field, the centre of gravity is identical to the centre of mass.
True or False?
The centre of mass of an object depends on the strength of the gravitational field it is in.
False.
The centre of mass does not depend on the gravitational field; it is the centre of gravity that depends on the field, since weight = mass × g.
Why does the Moon's centre of gravity shift towards Earth?
Because the centre of gravity depends on the gravitational field, and the Earth's stronger gravitational field pulls the Earth–Moon system's centre of gravity closer to Earth.

Sign up to unlock flashcards

By signing up you agree to our Terms and Privacy Policy

Previous:Scalars & VectorsNext:Equations of Motion