Forces

Pregunta	Respuesta
Force	A push or a pull
Contact Force	A force that is exerted directly on an object.
When does friction occur?	When 2 surfaces are pushed against each other so that their particles are in close contact.
Effects of friction	- Friction causes heat - Moving objects are slowed down - Surfaces wear
Lubricant	A substance that reduces friction between 2 moving surfaces
Static friction	The opposite frictional force that is at its maximum value and before the object starts to move
Sliding friction	The opposing frictional force that is slightly less than the static friction and the object moves at a constant speed.
Newton's 3rd Law	The mutual similar forces of action and reaction between 2 bodies are equal, opposite and collinear.
Nature of Force	- Forces may be attractive or repulsive. - Forces have both magnitude and direction.
Forces having magnitude and direction (vector)	If more than 1 force is applied, the combined effect of all the forces may keep the object stationary if the forces are balanced, or move the object if unbalanced.
Resultant Force	The single force that has the combined effect if all the forces operating on a body.
Hooke's Law	The extension of a spiral spring is directly proportional to the stretching force, provided that the spring is not stretched beyond its elastic limit
Rotation	The effect of a force when it is applied to a body which is free to move around a point.
Fulcrum/Pivot	The point about which rotation occurs.
Moment	The product of the force and the perpendicular distance of the line of action of the force form the pivot.
Moment (Formula)	T = Fd (T (tau) = moment, F = force, d = perpendicular distance)
Law of Moments	For a lever in equilibrium, the sum of clockwise moments equals the sum of anticlockwise moments.
A body is in equilibrium when:	- The resultant force is 0. - The sum of clockwise moments equals the sum of anticlockwise moments.
Centre of mass/gravity	The point at which the whole weight of the body is considered to act.
Position of centre of gravity	- It determines whether a body topples or not. - A body topples when the vertical line through its centre of mass falls outside of its base and has a moment which topples the body.
Stability of an object is increased by:	1. Lowering the centre of mass. 2. Increasing the are of the base.
Stable equilibrium	- The object returns to its initial position. - Centre of mass rises when displaced. - Weight has a moment around the point of contact (hence it rolling back).
Unstable equilibrium	- Object moves further away from its initial position when slightly displaced. - Centre of mass falls because it has a moment about the point of contact which increases displacement.
Neutral equilibrium	- The body remains in its new position after being displaced. - Weight acts through the point of contact, therefore, there is no moment to increase or decrease the displacement.
Lever	A device that can turn about a pivot.
Effort	The force applied to operate the lever.
Load	The resisting force.
1st class lever	- A lever that has the fulcrum between the effort and the load (EFL) - E.g. Scissors, see-saw, pliers
2nd class lever	- Load is between the effort and the fulcrum (ELF). - E.g. Wheelbarrow, nutcracker, bottle opener.
3rd class lever	_ Effort is between the load and the fulcrum. - E.g. Elbow, sugar tongs.
Resultant of a number of vectors	The single vector that will have the same effect as all the original vectors acting together.
Equilibriant of a number of forces	- The single force that keeps all the other forces in equilibrium. - It's equal in magnitude but opposite direction to the resultant of the forces.
Triangle Law	If 3 forces are in equilibrium, they van be represented in both magnitude and direction by 3 sides of a triangle taken in order.
Triangle Law	Image: 2ed23f8e-3ce2-43f8-a693-84ce4baeb407 (image/png)
Effect of force and mass on acceleration	Acceleration is: 1) Directly proportional to the resultant force for a fixed mass. 2) Indirectly proportional the mass for a constant force. - Therefore, F = ma
Newton's 2nd Law	When a resultant force is applied to a body, it produces an acceleration in the direction of the force that is directly proportional to the force and inversely proportional to the mass of the object.

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