# Using physics to make things work

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• Using physics to make things work
• Moments
• a moment is a turning force around a fixed point
• Pivot- the point around which the moment acts
• Load- the thing the moment is moving.
• Effort- the force applied to move it
• Affected by: increasing distance from pivot and increasing force
• Balancing moments
• Balance the force on each side of the pivot.
• Calculate the moment so that the anti-clockwise and clockwise moments are equal.
• Finding the mass of a beam
• Calculate moment from force to pivot.
• Work out where the centre of mass will be
• Divide the moment by (centre of mass minus distance from pivot).
• Pendulums
• Pendulums oscillate.
• Increasing the length of the pendulum increases the time period.
• Time period is how long it takes for the pendulum to complete one oscillation.
• Simple pendulum has: a mass (bob), and is suspended by string.
• Amplitude is the angle between the equilibrium and the position of the bob.
• Centripetal force
• A force which acts in a circular motion towards the centre of the circle.
• Not a force in it's own right as it is always caused by something else.
• Objects moving in a circle are accelerating because their velocity is changing all of the time.
• If the centripetal force stopped acting the object would continue moving at a tangent to the circle.
• Increasing: mass of the object, and speed of the object increases centripetal force needed for movement.
• Decreasing the radius of the circle increases the centripetal force needed.
• Centre of mass
• The point around which the mass of the object is thought to concentrate.
• Depends on the shape of an object
• A freely suspended object will come to rest with the centre of mass below the point of suspension.
• Hydraulics
• Uses the principle of pressure in liquids and that liquids can't be compressed.
• Used to move heavy loads whilst exerting low force.
• 1. Calculate the pressure on the slave piston using: pressure= force/ area.
• 2. Calculate the force exerted from the master piston using the same equation- remember pressure stays the same!
• Finding the centre of mass
• 1. stick a pin through the shape and secure in a clamp stand.
• 2. When it stops moving secure a plumb line from the same pin.
• 3. Mark the position of the plumb line on the object.
• 4. Repeat using a different point.
• 5. Centre of mass is where the lines marking the plumb line are.
• Pressure in liquids
• Pressure increases with depth
• Pressure is transmitted equally to all points in the liquid.