Using physics to make things work

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Moments

The moment of a force is a measure of the turning effect on the force on an object.

The moment of a force F = Fd (to increase the moment of a force, increase either F or d)

The weight of an object is called the load. The force applied to the lever is called the effort. The point about which the lever turns is called the pivot. The line along which a force acts is caalled the line of action.

Moment in balance

W1xD1 = W2xD2

For an object in equilibrium, the sum of the anticlockwise moments must equal the sum of the clockwise moments. The calculate the force needed to stop an object turning we use the above equation.

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Centre of mass

The centre of mass of an object is the point where its mass may be thought to be concentrated.

When a suspended object is in equilibrium, its centre of mass is directly beneath the point of suspension.

The centre of mass of a symmetrical object is along the axis of symmetry.

To keep an object stable, it's centre of mass must be above it's base. The object will topple if it's line of action is outside it's base (if it's resultant moment about it's point of turning is not zero).

The stability of an obet can be increased by increasing its base, or making its centre of mass as low as possible.

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Hydraulics

Pressure (pascal) = force/area  (if the force acting on the area is at right angles to the surface)

The pressure in a liquid acts evenly in all directions.

The force of a hydraulic system is much greater than the force applied to it.

F2 = F1/A1 x A2

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Circular motion

The velocity of an object moving in a circle at constant speed is continually changing as the object's direction is continually changing.

Centripetal acceleration is the acceleration towards the centre of the circle of an object that is moving round th circle.

The centripetal force depends on its mass, its speed and the radius of the circle.

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Pendulum

An oscillating motion is the motion of any object that moves to and fro along the same line.

The time period of a simple pendulum depends only on its length.

The amplitude of and oscillating object is the distance it moves from its equilibrium position to it's highest position

To measure the time period of a pendulum, we can measure the average time for 20 oscillations and divide the timing by 20.

Friction at the top of a playground swing and air resistance will stop it oscillating if it is not pushed repeatedly.

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