| Physics
4451 (Unit 3) - exam to be taken in June of Y11 |
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Written
paper 25% |
45 minutes - 45
marks
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PHY3H |
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| 13.1 |
How do forces have a turning
effect? |
Even if the forces acting on a body are balanced in the sense that they do not cause
the body to change speed, they can still make the body turn. |
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Candidates
should use their skills, knowledge and understanding of how science works:
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- to describe how to find the centre of mass of a thin sheet of a
material
- to calculate the size of a force, or its distance from an axis of
rotation, acting on a body that is balanced
- to analyse the stability of bodies by considering their tendency to
topple.
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Their skills,
knowledge and understanding of how science works should be set in these
substantive
contexts: |
- the turning effect of a force is called the moment.
- the size of the moment is given by the equation:
moment (newton metre, Nm )= force (newton, N) ×
perpendicular distance from the line of action of the force to the axis of rotation (metre, m)
- the centre of mass of a body is that point at which the mass of the body may be thought to be concentrated.
- If suspended, a body will come to rest with its centre of mass directly below the point of suspension.
- the centre of mass of a symmetrical body is along the axis of symmetry.
- If a body is not turning, the total clockwise moment must be exactly balanced by the total anticlockwise moment about any axis.
- recognise the factors that affect the stability of a body.
- If the line of action of the weight of a body lies outside the base of the body there will be a resultant moment and the body will tend to topple.
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