Circular motion, hydraulics, and Pendulums

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Circular motion

Why does an object moving in a circle accelerate?

When an object moves in a circle at a constant speed its velocity (which is a vector) is constantly changing. Its velocity is changing not because the magnitude of the velocity is changing but because its direction is. This constantly changing velocity means that the object is accelerating

 This is called centripetal acceleration.

What is the centripetal force?

For centripetal acceleration to happen there must be a resultant force acting toward the centre of the circle. This force is the centripetal force. 

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Circular motion


From looking at this equation it is clear that the size of the centripetal force depends on mass velocity and radius of circle.

In what cases does the centripetal force required to make an object perform circular motion increase?

  • If the mass of the object increases.
  • If the velocity of the object increases.
  • If the radius of the circle decreases.
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Why do hydraulics systems use liquids?

Liquids are used in hydraulic systems because they are incompressible.

How can hydraulic systems be used as force mulipliers?

Hydraulic systems can be used as force multipliers because the pressure on both sides is equal but the force is multiplied if the cross sectional area is larger on one side than the other.


P=pressure in pascals (N/m^2)

F=force in newtons

A=cross sectional area in metres squared

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What does the force exerted by a hydraulic system depend on?

Force (effort) exerted on system ---------- Area on which the effort acts on

As you go deeper into a liquid, the pressure increases. You can feel this on your ears as you swim down to the bottom of a swimming pool. We need to remember this when designing the walls of pools and dams: the wall must be thicker at the bottom, to withstand the increased pressure down there. We can use pressure in liquids to move a piston and do useful work. This is how the hydraulic systems in diggers, car brakes and fairground rides work: a pump creates pressure in an incompressible liquid, which acts on a piston. By adjusting the area of the piston, we can adjust the force we get.

Hydraulic system (

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Describe one complete oscilation of a pendulum.

A pendulum has completed one complete time period when it goes from left to right and back to the equilibrium position (middle point).

What factors affect the time period of a pendulum?

Length of the pendulum

Angle of release

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