Weight and circular motion (Edexcel GCSE Physics): Revision Notes

Weight and circular motion

Weight vs. Mass

• Mass is the same everywhere in the universe, no matter where you are (e.g., Earth, the Moon, or space).

• Weight depends on the gravitational field strength and changes depending on where you are (e.g., weight is different on the Moon compared to Earth). This is measured using a calibrated spring balance or a Newton meter.

Circular Motion

When an object moves in a circle at a constant speed, it is constantly changing direction and velocity.

• Since velocity includes both speed and direction, even if the speed is constant, a change in direction means the velocity is changing.

Centripetal Force:

• There must be a resultant force acting on the object to keep it moving in a circular path. This force is called the centripetal force.
• The centripetal force always acts towards the centre of the circle.
• Without this force, the object would move in a straight line (Newton's First Law).

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Examples of Centripetal Force:

• For a car going around a bend, friction between the tyres and the road provides the centripetal force.

  

• For a planet orbiting the Sun, gravitational force provides the centripetal force.

  

• For an object on a string being swung in a circle, the tension in the string provides the centripetal force.