Forces Flashcards
Principle of moments
when a lever is balanced, the sum of the clockwise moments about any point equals the sum of the anticlockwise moments about the same point
Balanced forces
Occur when there is no resultant force on an object
Newton’s first law
A body stays at rest, or if moving, it continues to make with uniform velocity, unless an unbalanced force makes it behave differently
Unbalanced forces
Occur when there is a resultant force causing an acceleration
Mass
Measured in KG shows amount of matter in an object
Newtons second law
Force = mass x acceleration
Friction
A force that always opposes motion
Weight
Force of gravity on an object
Acceleration of freefall
Acceleration of an object towards the surface of the Earth when the only force on it is the gravitational force
Gravitational field strength, g
Gravitational force on an object of mass 1 kg close to the surface of a planet
Equation for weight
Weight = force of gravity = mass X acceleration due to gravity
W = M x G
Gravity on the moon
1.6 N/kg
Deep space gravity
- No gravitational pulls
- G= 0
- everything is weightless
What will happen if there is no air resistance?
- The speed of a falling object will increase by 10 m/s every second
- acceleration = 10 m/s2
Hookes law
Extension is directly proportional to the applied load, up to a limit known as the limit of proportionality
What happens when a body is thrown vertically upwards?
- Motion is opposed by the force of gravity
- velocity of the body will decrease by 10m/s in each second until it’s vertical velocity = zero
Deceleration/retardation
Negative acceleration motion as opposed by force of gravity
What does hookes law describe?
behaviour of metal wires and springs when they are stretched or compressed
What is natural length in Hookes law?
Length of a spring, when no stretching or compressing forces are applied
Extension in hookes law
The difference between the stretch length of a spring, and it’s natural length
What do elastic materials do when the force is removed?
Returns to original length when stretching force is removed
What do plastic materials do when the stretching force is removed?
Do you not return to original length when the stretching force is removed
Hooks law equation
F = ke
K hooks law equation
- Spring constant
- N/CM or N/MM
- equal to gradient of force – extension graph
Pressure equation
P = F/A
Equilibrium
equilibrium is a state in which opposing forces or moments are balanced
Pressure
Force per unit on a surface
Centre of gravity
centre of gravity is the point through which the entire weight of a body appears to act
neutral equilibrium
neutral equilibrium is a state in which a slight displacement causes the object neither to move very far from its original position nor return to it le.g. a ball sitting on a bench)
unstable equilibrium
unstable equilibrium is a state in which a slight displacement causes the object to move a long way from its original position (e.g. a pencil balanced on its end)
stable equilibrium
stable equilibrium is a state in which a slight displacement causes the object to return to its original position (e.g. a traffic cone standing on its wide base)
What is necessary for maximum stability?
- The centre of gravity should be as low as possible.
- The area of the base should be as large as possible.
What is a moment?
The moment about a point is the product of a force and it’s perpendicular distance from the point
What is an incorrect direction of the moment?
Up or down, moments can only be clockwise or anticlockwise
Balanced force
If the object of stationary it will remain stationary, if it is moving, it will carry on moving at the same speed and in the same direction
Unbalanced forces
An unbalance force on an object, causes the object accelerate, according to F = MA
