Forces and Motion Flashcards
What is the Centre of Gravity
An imaginary point where the entire weight of an object appears to act
What is the Centre of Mass
A point through which any externally applied forces produces a straight line motion but no rotation
What Idea is the Centre of Gravity Practical Based on?
A freely suspended object will come to rest with its centre of gravity vertically below the point of suspension
What is the moment of the force dependent on?
• The magnitude of the force acting• The perpendicular distance from the pivot that the forces act
Moments Equation
Moment = Force x Perpendicular Distance M = Fd
What does it mean if an object is in equilibrium? (Principle of Moments)
The sum of the clockwise moments about a pivot must equal the sum of the anti-clockwise momentsIt makes no difference at which point the moments are taken
What is a couple?
Two forces that are equal and opposite to each other but are not on the same straight line
Torque Equation
Torque = One of the forces x perpendicular distance between both forces 2 x F x 1/2d = ↩️A = Torque
What is Kinetic Energy?
Where movement is taken place
What is Potential Energy?
Regions where electric, magnetic, gravitation, and nuclear forces exist
What is Energy?
The capacity to do work
What is a Joule?
1 Joule is the energy transferred in a moving force of 1N through a distance of 1m
What is Gravitational Potential?
The capacity for an object to do work as a result of its position in a gravitational field
What is Power?
The power generated by a force is the rate at which it does work
Power Equation?
Power = Work Done/ TimeP = W/t
What is a Watt?
One watt is the power generated when one joule of energy is transferred per second
What is Efficiency?
Useful Power Output/ Power Input
What is Newton’s First Law? (Law of Inertia)
A body will remain at rest or continue to move at a constant velocity unless acted on by a resultant force
What is Inertia?
The resistance a body has to a change in state of motion
What is Linear Momentum?
Product of an objects mass and velocity
Momentum Equation
Mass x Velocity = Momentum p = mv
What is the derivation of the Change in Momentum?
P = mv - mu P/t = (mv - mu)/t = m((V-u)/t)= ma = FThe change in momentum = Force
What is Newton’s Second Law?
The rate of change of momentum of an object is directly proportional to the resistant force and takes place in the direction of the force
What is Newton’s Third Law?
If body A exerts a force on body B then body B exerts a force in body A that is:• Equal in magnitude • Of the same type• In the opposite direction
What is the Impulse?
The product of the magnitude of the force and the length of time it’s appliedThe impulse is equal to the area under the F/t graph
What is the Conservation of Momentum?
For a system of interacting objects the total momentum of a specified direction remains constant as long as no external forces act on the system
What is an Elastic Collision?
The total kinetic energy and momentum of the system are conserved In an inelastic collision kinetic energy is not conserved whilst momentum is
What happens in an Explosion?
In an explosion the vector sum of all the momenta of individual fragments is 0
What’s an Oblique Collision?
When two objects of equal mass collide in a non head on elastic collision they will always move away at 90° from each other
What is Hooke’s Law?
The force in a solid is proportional to the applied extension within the elastic limit of that solid F = Kx
What is the Elastic Limit
The maximum extent to which a solid may be stretched without permanent alteration
Elastic Deformation?
Deformation that is fully reversed when the load is removed
What is Plastic Deformation?
The permanent deformation result in from tensile stresses exceeding its elastic limit
What is Elastic Potential?
When a spring is deformed work is done —> Energy is stored in the deformed material as elastic potential Equal to the work done when producing an extension or compressionE = 1/2Kx^2
What is Stress?
The force applied per unit across a cross sectional area = F/A Can be tensile or compressive
What is Strain?
The fractional change in length under load= x/L
What is Ultimate Tensile Strength?
The maximum stress a material can stand when being stretched before breaking
What does bring a Brittle Material mean?
Can with stand large forces whilst experiencing little deformation but will break beyond their elastic limit
What does being a Ductile Material mean?
Can be stretched beyond their elastic limit without breaking
What is Polymeric Behaviou?
Material made of any smaller molecules bonded together often made of tangled chains. The polymer chains can be unravelled as the rubber is stretched after a point the rubber becomes more still and difficult to extend
What is the Young Modulus?
A constant for a given material and is a measure of its stiffness given by the gradient of a stress strain graph Young Modulus = Stress/Strain
What is Archimedes’ Principle?
The upthrust exerted on a body immersed in a fluid is equal to the weight of the fluid that the body displaces
