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AS Physics: forces & motion definitions

Listed below are all the definitions you need to know in the Forces and Motion unit. This means you must be able to write them down in the examination and understand them.

The concept being defined is in bold type, for example the first line below defines a scalar quantity. Once you've learned them, print out our list of definition names.

Need to Know Definitions

    A scalar quantity has magnitude only. [tutorial]

    A vector quantity has magnitude and direction. [tutorial]

    Displacement is distance travelled in a specific direction.

    Velocity is rate of change of displacement.

    Acceleration is rate of change of velocity.

    Mass is the property of a body that resists change in its motion.

    Density = mass/volume

    1 Newton is the force that causes an object of mass 1 kg to accelerate at 1 ms-2.

    Weight is the effect of a gravitational field on a mass.

    Pressure is the force per unit area.

    Moment of a force about a pivot = Force × perpendicular distance between the line of the force and the pivot.

    Torque of a couple = Fd (distance between lines of the forces is d and each force is F.)

    The principle of moments states that for an object in equilibrium, the sum of the clockwise moments about a point equals the sum of the anticlockwise moments about the same point.

    The centre of gravity is the point through which the weight appears to act.

    Work is force multiplied by distance moved in the direction of the force.

    1 joule of work is done or 1 J of energy is transferred when a force of 1 N moves though a distance of 1 m.

    The principle of conservation of energy: energy is neither created nor destroyed. It is converted from one form to another.

    Power is the rate of doing work or the rate of converting energy.

    1 watt is the power when 1 joule of work is done per second.

    An object obeys Hooke's law if the extension is proportional to the load.

    Elastic behaviour is when the sample returns to its original length when a load is removed.

    Plastic behaviour is when the sample does not return to its original length when loads are removed.

    Stress is force per unit area.

    Strain is extension per unit length.

    Young modulus is the ratio of stress/strain.

    Ultimate tensile stress (U.T.S.) is the maximum stress when the sample brakes.

Learning Techniques

The problem with need to knows is there's no easy way of learning them. You have to sit down, read them, then write them out again.

Print out our list of definition names. Come back to this after you've gone through 6 or 7 definitions and write out, from memory, the definitions. Check them afterwards!

Repeat this until you've completed the list and are happy. Come back to the same list and test yourself a week later. See how many you can remember!

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© 2006 A P Harmsworth. All rights reserved. E&OE. Bookmark. Advertise. GCSE revision.