Return to 1 Forces and Motion – Part A “Units”

1 Forces and Motion – Part C2b “Momentum and Moments”

Aims… (Triple Only)

1.25P know and use the relationship between momentum, mass and velocity:

momentum = mass × velocity      OR    p = mv

1.26P use the idea of momentum to explain safety features

1.27P use the conservation of momentum to calculate the mass, velocity or momentum of objects

1.28P use the relationship between force, change in momentum and time taken: 

force = change in momentum/time taken 

F = (mv-mu)/t

1.29P demonstrate an understanding of Newton’s third law.

1.30P know and use the relationship between the moment of a force and its distance from the pivot:

moment = force × perpendicular distance from the pivot

1.31P know that the weight of a body acts through its centre of gravity

1.32P use the principle of moments for a simple system of parallel forces acting in one plane

1.33P understand how the upward forces on a light beam, supported at its ends, vary with the position of a heavy object placed on the beam.


This PowerPoint of resources covers most of the key ideas in the unit…

Extra Resources

Video Clips…

Moments and Centre of Mass of a Bird iGCSE Physics

In physics, the centre of mass of (sometimes referred to as the balance point) is the unique point where the weighted relative position of the distributed mass sums to zero. ...

In the case of a single rigid body, the centre of mass is fixed in relation to the body, and if the body has uniform density, it will be located at the centre. The centre of mass may be located outside the physical body, as is sometimes the case for hollow or open-shaped objects, such as a horseshoe.

In the case of a distribution of separate bodies, such as the planets of the Solar System, the centre of mass may not correspond to the position of any individual member of the system.

In terms of this bird the COM occurs on the tip of the birds nose as the wings are weighted with moments to counterbalance the tail mass. There would be one moment acting at the tail of force x distance. This counterposes the force x distance of each of the wing weights. They act around the pivot point of the nose to balance out.

The principle of moments is that the anticlockwise moments balance the clockwise moments for an object in equilibrium.
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