Moments, levers and gears Flashcards
Moment
The turning effect of a force
A measure of an objects tendency to rotate when a force is applied
What are clockwise and anticlockwise moments?
When the movement caused by a moment is anti-clockwise, it is an anti-clockwise moment
When the movement caused by a moment is clockwise, it is a clockwise moment
Pivot/ fulcrum
A point where something can rotate or turn around
Perpendicular distance
The shortest distance between the pivot and the line of action of the force
Line of action
Representation of how the force is applied using lines
How to calculate a moment?
Moment (Nm) = force (N) x perpendicular distance to the pivot (m)
What is the moment of a balanced object?
The clockwise moment = anti-clockwise moment
What are levers?
A tool used to transmit the turning effect of the force
Used so we apply an input force, and the lever creates a larger output force so we don’t have to do as much work
Examples of levers
Scissors
See saws
Wheelbarrows
Spanner/hammer and a nut
What happens to input and output forces if they are on different sides of the pivot?
They work in different directions, like in scissors
What happens to input and output forces if they are on the same side of the pivot?
Act in the same direction eg in a wheelbarrow
Why is the output force closer to the pivot than the input force?
So the output force is stronger, which is the whole point of a lever
Shown in the equation force = momentxdistance
Work
When a force is done on an object energy is transferred
Eg pushing a box transfers kinetic energy to thermal energy in friction
Elastic material
Applying more than 1 force to compress or stretch an object then returns to its original shape
Force needed to stretch object
Spring constant x extension/compression
What happens when material is stretched?
We do work by transferring energy
And storing it as elastic potential energy
How to work out weight of object based on extension caused?
Measure extension of spring to line on graph then to the weight
Extension and weight with a spring and rubber band
Spring = Directly proportional and a linear relationship
Rubber band = s shape and non linear relationship
Adding too much weight
Extension no longer linear because overstretched
So not return to original shape
= exceeded limit of proportionality
Inelastic deformation
Won’t return to original shape
Particles in a fluid
Exert a force at right angles to the container
Pressure unit
Pa
Pressure equation
Normal to surface (N) / area of that surface (m2)
Pressure in a liquid container
Higher at the bottom
Because greater weight of liquid acting downwards
And so greater density of liquid
Object float or sink
Bottom of object has larger pressure than top as it has a higher depth
So larger force on bottom than too
Resultant force UP = upthrust
It will float if upthrust = weight
It will sink if upthrust = less than weight
Why does water rise when object put in?
Because it is displaced by the object
Size of upthrust and displacement
Size of upthrust acting on object is the same as water displaced by the object
