4.4.2

Force in Uniform Fields

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Force on a Mass in a Uniform Gravitational Field

Objects with mass feel a force when they are placed in a uniform gravitational field. This force is called the weight of the object.

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Uniform gravitational field

  • The gravitational field lines of the Earth are directed radially inwards towards the centre of the Earth.
  • Near the surface of the Earth, the field lines are approximately parallel.
  • We can consider the gravitational field of the Earth as being a uniform field close to the surface.
    • The magnitude of the gravitational field strength gg near the surface of the Earth is approximately constant and equal to 9.8 m/s.
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Weight

  • A particle of mass mm in a uniform gravitational field feels a force WW that is given by:
    • W=m×gW=m\times g
  • This force is known as the weight of the object.

A Uniform Electric Field

A uniform field is one which has the same strength at every point in the field.

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Uniform field

  • A uniform field has the same strength everywhere, it can be made from parallel charged plates.
  • If two charged plates are held a distance apart the field between them will be uniform
    • The field lines will travel straight from the positive plate into the negative plate.
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Calculating the field

  • If two plates are held apart with different charges they will have a voltage difference between them. The equation for the field strength is:
    • Field strength = voltage drop ÷ distance between the plates
    • E=V/dE=V/d
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Force on a charged particle

  • Similarly to an object of mass in a uniform gravitational field, a charged particle feels a force in a uniform electric field.
  • The force is equal to the size of the charge qq multiplied by the strength of the electric field EE:
    • F=E×qF=E\times q

Jump to other topics

1Physical Quantities & Units

2Measurement Techniques

3Kinematics

4Dynamics

5Gravitational Fields

6Deformation of Solids

7Thermal Physics

8Oscillations

9Communication

10Electric Fields

11Current Electricity

12Magnetic Fields

13Modern Physics

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