Moments (Edexcel GCSE Physics): Flashcards
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What is meant by the moment of a force?
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What is meant by the moment of a force?
A moment is the turning effect of a force about a pivot.
What is the equation for calculating the size of a moment?
M* = *F* × *d
where M is the moment in newton metres (N m), F is the force in newtons (N), and d is the perpendicular distance of the force to the pivot in metres (m).
The distance d used in the moment equation must be the ______ distance of the force to the pivot.
The distance d used in the moment equation must be the perpendicular distance of the force to the pivot.
Why is a door handle placed on the opposite side of the door to the hinge?
Placing the handle far from the hinge (the pivot) increases the perpendicular distance, d, so a given force creates a larger moment, making the door easier to open.
What is a couple?
A couple is a pair of forces that are equal in size and opposite in direction, which do not act through the same point, causing an object to rotate.
True or False?
A moment can only be caused by a single force acting on an object.
False.
A system of forces can also cause an object to rotate, for example a couple, where two equal and opposite forces act without passing through the same point.
State the principle of moments.
If an object is balanced, the total clockwise moment about a pivot equals the total anticlockwise moment about that pivot.
On a balanced horizontal beam, which forces produce a moment?
Forces that are perpendicular to the distance from the pivot, for example forces directed upwards or downwards on the beam.
For a balanced beam, total clockwise moments ______ total anticlockwise moments.
For a balanced beam, total clockwise moments equal total anticlockwise moments.
A parent (690 N) sits 0.3 m from the pivot of a see-saw. Their child provides a clockwise force of 140 N. How far from the pivot must the child sit to balance the see-saw?
Anticlockwise moment = 690 × 0.3 = 207 N m
At balance, 140 × d = 207
d = 207 ÷ 140 = 1.48 m
True or False?
When applying the principle of moments, distances can be left in different units (e.g. some in cm, some in m).
False.
All distances must be converted to the same units before applying the principle of moments.
When describing the effect of a turning force, how is the direction defined?
A turning force can cause rotation about a pivot in a clockwise or anticlockwise direction.
Clockwise is the direction in which the hands of a clock move; anticlockwise is the opposite direction.
What do lever and gear systems use to transmit and amplify the rotational effects of forces?
The concept of moments.
Give two ways to make a lever more effective.
Increase the size of the force applied
Increase the distance of the force from the pivot
How does a bottle opener use moments to remove a bottle top?
The small force applied by the person acts much further from the pivot than the large force needed at the bottle cap, so the lever amplifies the small force into a large force on the cap.
In a gear system, the toothed wheels rotate on an axle or shaft, which acts as the ______.
In a gear system, the toothed wheels rotate on an axle or shaft, which acts as the pivot.
If a larger gear is driven by a smaller gear, how does the larger gear's rotation and moment compare to the smaller gear's?
The larger gear rotates slower than the smaller gear but has a greater moment.
True or False?
When two gears mesh together, they rotate in the same direction.
False.
One gear rotates clockwise and the other rotates anticlockwise, since their teeth move in the same direction where they meet.
Why do two meshed gears of different sizes experience the same force but different moments?
The force is the same on both gears, but the moment differs because the distance from the teeth to each gear's own pivot (axle) depends on the gear's size.
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