# Physics Section 3 Key Terms

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acceleration
The rate of change of velocity, vector
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acceleration of free fall
The rate of change of velocity of an object falling in a gravitational field, symbol g
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Air Resistance
The drag or resistive force experience by objects moving through air
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Archimedes' principle
The upthrust on an object is equal to the weight of fluid it displaces
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Average Speed
The rate of change in distance calculated over a complete journey
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Average Velocity
The change in displacement for a journey divided by the time taken
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Braking Distance
Distance travelled by a vehicle from the time the brakes are applied until the vehicle stops
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Breaking Stress
The stress value at the point of fracture, calculated by dividing the breaking force by the cross sectional area
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Brittle
Property of a material that does not show plastic deformation and deforms very little under high stress
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Centre of Gravity
An imaginary point at which the entire weight of an object appears to act
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Centre of Mass
A point through which any externally applied force produces straight-line motion but no rotation
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Closed System
An isolated system that has no interaction with its surroundings
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Compression
The decrease in length of an object when a compressive force is exerted on it
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Compressive deformation
A change in the shape of an object due to compressive forces
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Compressive Force
Two or more forces together that reduce the length or volume of an object
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Constant Speed
Motion in which the distance travelled per unit time stays the same
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Constant Velocity
Motion in which the change in displacement per unit time stays the same.
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Couple
A pair of equal and opposite forces acting on a body, but not in the same straight line
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Density
The mass per unit volume of a substance
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Displacement
The distance travelled in a particular direction, vector
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Drag Force
The resistive force exerted by a fluid on an object moving through it
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Ductile
Property of a material that has a large plastic region in a stress-strain graph, so can be drawn into wires.
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Elastic Deformation
A reversible change in the shape of an object due to a compressive or tensile force- removal of stress or force will return the object to its original shape and size
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Elastic Limit
The value of stress or force beyond which the elastic deformation becomes plastic deformation, and the material or object will no longer return to its original shape and size when the stress or force is removed
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Elastic Potential Energy
The energy stored in an object because of its deformation
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Energy
The capacity for doing work, measured in joules
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Equilibrium
A body is in equilibrium when the net force and net moment acting on it are zero
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Extension
The increase in length of an object when a tensile force is exerted on it
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Fluid
A substance that can flow, including liquids and gases
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Force
A push or pull on an object, measured in Newtons
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Force Constant
A quantity determined by dividing force by extension/compression for an object obeying Hooke's lawcalled constant of proportionality 'k' in Hooke's Law, measured in Nm-1
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Force-Extension Graph
A graph of force against extension/compression with the area under the graph equal to the work done on the material
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Force-time Graph
A graph of net force against time, with the area under the graph equal to the impulse
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Free Fall
The motion of an object accelerating under gravity with no other force acting on it
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Free-body diagram
A diagram that represents the forces acting on a single object
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Gravitational Potential Energy
The capacity for doing work as a result of an object's position in a Gravitational Field
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Hooke's Law
The force applied is directly proportional to the extension of a spring unless the limit of proportionality is exceeded
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Hysteresis Loop
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Impulse
The area under a force-time graph, the product of force and the time for which the force acts
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Inelastic Collision
A collision in which kinetic energy is lost
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Instantaneous Speed
The speed at the moment it is measured- speed over an infinitesimal interval of time
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Kinetic Energy
The energy associated with an object as a result of its motion
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Limit of proportionality
The value of stress or force beyond which the stress is no longer directly proportional to strain
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Linear Momentum
A property of an object travelling in a straight line, the product of its mass and velocity, measured in kgms-1 or Ns
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A force-extension graph
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Mass
Amount of matter, measured in kilograms
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Moment
The product of force and perpendicular distance from a pivot or stated point
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Newton's First Law of Motion
A body will remain at rest or continue to move with constant velocity unless acted upon by another resultant force
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Newton's Second Law of Motion
The rate of change of momentum of an object is directly proportional to the resultant force and takes place in the direction of the force (F=ma)
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Newtons Third Law of Motion
When two objects interact, each exerts an equal but opposite force on the other during the interaction
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Normal Contact Force
The force exerted by a surface on an object, which acts perpendicularly to the surface
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Perfectly Elastic Collision
A collision in which no kinetic energy is lost
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Pivot
A point about which a body can rotate
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Plastic Deformation
An irreversible change in the shape of an object due to a compressive or tensile force- removal of the stress or force produces permanent deformation
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Plumb-line
A string with a weight used to provide a vertical reference line
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Polymeric
Description of a material comprising of long-chain molecules, such as a rubber, which may show large strains.
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Power
Rate of work done, measured in watts
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Pressure
The force exerted per unit cross-sectional area, measured in pascals
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Principle of conservation of energy
The total energy of a closed system remains constant- energy cannot be created nor can it be destroyed
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Principle of conservation of momentum
Total momentum of a system remains the same before and after a collision
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Principle of Moments
For a body in rotational equilibrium, the sum of the anticlockwise moments about a point is equal to the sum of the clockwise moments about the same point
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Projectile
An object that is thrown or propelled on the surface of the Earth
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Restoring Force
A force that tries to return a system to its equilibrium position
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Stiffness
The ability of an object to resist deformation
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Stopping Distance
The total distance travelled from the time when a driver first sees a reason to stop to the time when the vehicle stops, the sum of thinking distance and braking distance
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Strong Material
A material with a large value for the ultimate tensile strength
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Tensile Deformation
A change in the shape of an object due to tensile forces
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Tensile Force
Equal and opposite forces acting on a material to stretch it
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Tensile Strain
The extension per unit length, a dimensionless quantity
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Tensile Stress
The force per unit cross-sectional area, measured in Pascals
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Tension
The pulling force exerted by a string, cable or chain on an object
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Terminal Velocity
The constant speed reached by an object when the drag force and upthrust is equal and opposite to the weight of the object
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Thinking Distance
The distance travelled by a vehicle from when the driver first perceives a need to stop to when the brakes are applied
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Time of Flight
The time taken for an object to complete its motion
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Torque of a Couple
The product of one of the forces of a couple and the perpendicular distance between the forces
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Ultimate Tensile Strength
The maximum stress that a material can withstand before it breaks
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Uniform Gravitational Field
A gravitational field in which the field lines are parallel and the value for g remains constant
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Upthrust
The upward buoyant force exerted on a body immersed in a fluid
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Velocity
A vector quantity equal to the rate of change of displacement
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Weight
The gravitational force on an object, measured in Newtons
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Work
The product of force and distance moved in the direction of force, measured in Joules
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Yield Point
A point on a stress-strain graph beyond which the deformation is no longer entirely elastic
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## Other cards in this set

### Card 2

#### Front

The rate of change of velocity of an object falling in a gravitational field, symbol g

#### Back

acceleration of free fall

### Card 3

#### Front

The drag or resistive force experience by objects moving through air

### Card 4

#### Front

The upthrust on an object is equal to the weight of fluid it displaces

### Card 5

#### Front

The rate of change in distance calculated over a complete journey