Sectieoverzicht

  • So far, we have learnt a lot about forces. We know that...

    • A force is a push or a pull that results from the interaction between two objects.
    • Interactions can involve direct contact or occur at a distance. We can have contact interactions and non-contact interactions.
    • Therefore, there are contact forces and non-contact forces.

      • Examples of non-contact forces are gravity, magnetic force and electric force.
      • Examples of contact forces include the normal force, friction, tension, air or water resistance, the spring force and applied force.

    • Forces act in interacting pairs on an object.
    • We cannot see a force, only its effects.
    • Force is a vector: it has both size and direction.

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      The Effects of Forces

      Have a look at the following pictures and try and describe how the forces acting on each object are changing that object or its properties.

      How is the person's hand changing the ball?
      Stress ball

      What effect does the force applied by the truck's brakes have?
      Braking

      What happens does the player use his head to do to the ball?
      Header

      In the first case, the person uses their hand to squeeze the ball. This force changes the ball's shape.

      In the second case, the force applied by the truck's brakes act to slow the truck down to a stop. In other words, they change the speed of the truck.

      In the last case, the player uses his head to apply a force to the ball to change its direction.

      When an object is moving, we say it has a velocity. Velocity is the speed of an object AND its direction. Speed describes only how fast an object is moving, whereas velocity gives both speed and direction.

      An object can move at constant velocity. This means it travels at the same speed in the same direction. For example a car travelling along the highway at 100 km/h in a straight line has a constant velocity. However, what happens when the car accelerates or brakes? It's speed and, therefore, velocity changes.

      If the same car changes lanes, its velocity will also change even if its speed does not because its direction has changed. Therefore,

      • Forces can change the shape of an object. This is called deformation.
      • Forces can change the velocity of an object. This means that either the object's speed or direction (or both) are changed.

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      Watch: How Objects Interact

      Watch the following video for an excellent summary of what we have learnt about forces.

    • Forces quiz Test
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