Physics AS definitions
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Physics AS definitions - Leaderboard
Physics AS definitions - Details
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| Average speed | Total distance travelled by an object divided by the total time taken |
| Instantaneous speed | The speed of an object measured over a very short period of time |
| Displacement | The distance travelled in a particular direction; it is a vector quantity |
| Vector quantity | A quantity with both magnitude and direction |
| Scalar quantity | A quantity with magnitude only |
| Velocity | The rate of change of an object's displacement |
| Vector triangle | A triangle drawn to determine the resultant of two vectors |
| Resultant vector | The single vector formed by adding together two or more vectors |
| Acceleration | The rate of change of velocity of an object; the unit is m/s² |
| Constant acceleration | When the change in velocity of an object is the same in the same time period; sometimes called uniform acceleration |
| Uniform acceleration | When the change in velocity of an object is the same in the same time period |
| Non-uniform acceleration | When the velocity of an object changes by different amounts in the same period of time |
| Tangent | A straight like that touches a curve but does not cross it at a point |
| Free fall | When an object accelerates due to gravity in the absence of any other forces such as air resistance |
| Component | The effect of a vector along a particular direction |
| Newton's second law of motion | Resultant force is proportional (or equal) to mass x acceleration/rate of change of momentum |
| Weight | The force on an object caused by a gravitational field acting on its mass |
| Friction | The name for a resistive force when two surfaces are in contact and tending to slide over one another |
| Centre of gravity | The point where the entire weight of an object appears to act |
| Uniform motion | The natural state of motion of an object-uniform velocity, constant speed and direction |
| Newton's first law of motion | An object will remain at rest or in uniform motion unless acted on by a resultant force |
| Resultant force | The single force that has the same effect as all of the forces acting on an object |
| Terminal velocity | The maximum velocity reached by an object falling under gravity or accelerated by a constant force |
| Resistive force | A backwards force in the opposite direction to movement caused by friction ot some other viscous force |
| Drag | A force that resists the movement of a body through a fluid |
| Contact force | The force perpendicular to a surface when two objects are in contact |
| Upthrust | The force upwards in a liquid or gas caused by the pressure in the gas or liquid |
| Newton's third law of motion | When two bodies interact, the forces they exert on each other are equal in size and opposite in direction |
| Base units | Defined units of the SI system from which all other units are derived |
| Derived units | Units that are combinations of the base units of the SI system |
| Newton | One newton is the force that will give 1kg mass an acceleration of 1m/s² in the direction of the force |
| Homogenous | Equations with the same base units on each side are homogenous |
| Mass | The quantity of matter which a body contains |
| Resultant force | The single force that has the same effect as all of the forces acting on an object |
| Triangle of forces | A closed triangle drawn for an object in equilibrium. The sides of the triangle represent the forces in both magnitude and direction. |
| Equilibrium | An object in equilibrium is either at rest or travelling with a constant velocity because the resultant force on it is zero |
| Components (of a vector) | The magnitudes of a vector quantity in two perpendicular directions |
| Resolving (the vector) | To split a vector (such as a force) into two vectors at right angles |
| Free-body force diagram | A diagram showing all the forces acting on an object (but not the forces it exerts on other objects) |
| Centre of gravity | The point where the entire weight of an object appears to act |
| Moment of a force | The product of the force and the perpendicular distance from the line of action of the force to the point |
| Principle of moments | The sum of the clockwise moments about a point is equal to the sum of the anticlockwise moments about the same point provided the body is in equilibrium |
| Couple | A pair of equal and opposite forces that act on an object at different points and produce rotation only |
| Torque (of a couple) | The product of one of the forces and the perpendicular distance between the forces |
| Energy | A calculated quantity that is conserved during any change; that which is transferred when a force does work |
| Joule | The work done when a force of 1N moves a distance of 1m in the direction of the force |
| Gravitational potential energy, Ep | The energy a body has due to its position in a gravitational field |
| Principle of conservation of energy | Energy cannot be created or destroyed. It can only be changed from one form to another |
| Power | Rate at which a device does work per unit of time |
| Watt | One watt is one joule per second |
| Work | When a force moves (displaces) the body in the direction of the force; energy is then transferred from one body to another |
| Potential energy | The energy an object has because of its position or shape |
| Linear momentum | The product of its mass and velocity |
| Closed system | A system of interacting objects in which there are no external forces |
| Conservation of momentum | The sum or total momentum of the bodies in a closed system is constant provided no resultant external force acts |
| Perfectly elastic (collision) | The total kinetic energy of all the bodies remains constant |
| Inelastic (collision) | Kinetic energy is not conserved; some is transferred to other forms such as heat |
| Newton's first law of motion | An object remains at rest or travels at constant velocity unless it is acted on by a resultant force |
| Newton's second law of motion | The resultant force on a body is proportional (or equal) to the rate of change of momentum of the body |
| Newton's third law of motion | When body A produces a force on body B then body B produces an equal and opposite force on body A |
| Density | Mass per unit volume |
| Pressure | The normal (or perpendicular) force acting per unit cross-sectional area |
| Archimedes' principle | The upthrust acting on a body is equal to the weight of the liquid or gas that it displaces |
| Compressive | Describes a force that squeezes and shortens an object |
| Tensile | Associated with tension or pulling; for example, a tensile force |
| Extension | The increase in the length of a material from its original length |
| Spring constant | The force per unit extension for a spring; unit is N/m |
| Hooke's law | Provided the elastic limit is not exceeded, the extension of an object is proportional to the applied force (load). |
| Elastic deformation | An object that returns to its initial length when the force is removed has deformed elastically |
| Plastic deformation | An object that does not return to its initial length when the force is removed is deformed permanently - it has deformed plastically |
| Limit of proportionality | The point beyond which extension (of a spring) is no longer proportional to the force |
| Elastic limit | The value of stress beyond which an object (such as a spring) will not return to its original dimensions |
| Strain | Extension per unit length |
| Stress | Force per unit cross-sectional area that acts at right angkes to a surface |
| Young modulus (of a material) | The stress in the material divided by the strain |
| Elastic potential energy | Energy stored in a body due to a change in its shape |
| Strain energy | Energy stored in a body due to a change in its shape |
| Work done | The product of the force and the distance moved in the direction of the force; the area under a force extension graph |