what is needed for an object to rotate?
a pivot, a force
define a moment
the measure of its turning effect, about a pivot
if the force applied to the object remains constant, how would the moment increase?
increase the perpendicular distance from the pivot
what is the equation to calculate the moment of an object?
force (N) x perpendicular distance from point to force (m)
are moments scalar or vector?
a vector (either anticlockwise or clockwise)
where would the principle of moments be present?
on a see-saw
where any body is in equilibrium
what happens when the principle of moments holds true?
no accelerating = nothing is turning = no resultant moment acting about a point
equation to see an object is in equilibrium (moments)
sum of anticlockwise moments = sum of clockwise moments
what is a key concept to remember when calculating moments?
must take into account PERPENDICULAR distance from pivot
explain what a lever does
- acts as a force multiplier
- so a small effort (force) can be applied to one side + a larger effort is exerted on the opposite side of the pivot
what is mechanical advantage?
a measure of force amplification achieved by a tool
so a lever’s mechanical advantage must always be greater than 1
equation to calculate mechanical advantage (of a lever)?
explain how a gear acts
- as a moment multiplier
how do gears multiply moments?
as the perpendicular distance changed from the load to the pivot (radius of pivot)
FORCE STAYS SAME
equation to calculate mechanical advantage (of a gear)?
input cog radius
again, must be greater than 1 (is a multiplier)
how do gears transmit forces?
- basically rotating levers
- small cog makes larger cog rotate with same force (passed by teeth)
- but radius is greater = a greater perpendicular distance = a greater moment
at what angle do pressures exert forces to any surface?
what is the equation to calculate pressure?
what is the unit for pressure?
when a force is applied to water it transmits it ………….. in all …………….
define a hydraulic machine
a force multiplier that uses a liquid to transmit a force
does the pressure change within a hydraulic machine?
no, the pressure applied to the master piston is equal to the slave piston (as liquids cannot be compressed)
how do hydraulic brakes act as a force multiplier?
they increase the force by increasing the area of the slave piston compared to master piston
p = f/a, pressure remains constant, so a higher area means a greater force is applied
what is the main reason why hydraulic machines can act as force multipliers?
as pressure is constant for fluids (exerts an equal force in all directions)
- so greater area = greater force (to keep pressure constant)