Forces

• Force is a vector quantity
• Force is measured in newtons (N)
• Equal forces in opposite directions are balanced
• Newtons first law: An object will remain at rest or in motion unless acted upon by a resultant force
• Balanced forces occur when there is no resultant force on the object
• Unbalanced forces occur when there is a resultant force causing acceleration
• Newtons second law: The acceleration of an object is directly proportional to the resultant force acting on it
• Force = mass x acceleration
• Friction is the force that always opposes motion
• Mass is the amount of matter in an object (kg)
• Weight is the force of gravity on an object (N)
• weight = mass x gravity
• On earth the gravitational force is 10 N/KG
• Acceleration = force / mass (m/s2)
• All objects in the absence of air resistance fall at a rate of 10 m/s
• Gravitational field strength = weight / mass
• When an object is thrown vertically upwards, its motion is opposed by the force of gravity. The velocity will decrease by 10 m/s until it reaches 0.
• Negative acceleration is called retardation
• Hooke's law states that the extension of an object is directly proportional to the force applied to it
• force = extension x spring constant
• The natural length is the length of the spring when no compressing or stretching forces are applied.
• The extension is the difference between the stretched and natural length.
• Pressure = force / area
• presure is measured in Pa or N/cm2
• The centre of gravity is the point which the entire weight of an object appears to act
• Equilibrium is when the opposing forces and moments are balanced.
• A neutral equilibrium is when slight displacement causes an object to move neither far from nor return to its original position.
• An unstable equilibrium is a state when a slight displacement causes the object to move a long way from its original position.
• A stable equilibrium is a state where a slight displacement causes an object to return to its original position
• Moments have either anticlockwise or clockwise direction
• moment = force x distance to pivot#
• Moments are measured in Ncm
• The principle of moments law states that when a level is balanced, the sum of the clockwise moments is equal to the sum of the anticlockwise moments about the same point.
• Upwards forces must balance downwards forces