Forces - Key Terms

• Scalar


  a quantity, such as time or temperature, that has magnitude but no direction
• Vector


  a variable quantity that has magnitude and direction
• Force


  an influence that occurs when two objects interact
• Contact force

  a force that occurs between two objects that are in contact (touching), e.g. friction and tension
• Non-contact force


  a force that occurs between two objects that are not in contact (not touching), e.g. gravitational and electrostatic forces
• Gravity


  the force of attraction exerted by all masses on other masses, only noticeable with a large body, e.g. the Earth or Moon
• Mass


  a measure of how much matter an object contains, measured in kilograms (kg)
• Weight

  the vertical downwards force acting on an object due to gravity
• Resultant


  a single force that represents the overall effect of all the forces acting on an object
• Free body diagram


  a diagram used to show the relative magnitude and direction of all the forces acting on an object in a given situation
• Work


  the product of force and distance moved along the line of action of the force, when a force causes an object to move
• Elastically deformed


  describes an object that can return to its original shape when the forces causing it to change shape are removed
• Inelastically deformed


  describes an object that cannot return to its original shape when the forces that caused it to change shape are removed (because the limit of proportionality has been exceeded)
• Extension


  the distance over which an object (like a spring) has been extended / stretched
• Limit of proportionality


  the point up to which the extension of an elastic object is directly proportional to the applied force (once exceeded the relationship is no longer linear)
• Compression


  the act of squeezing / pressing (an elastic object)
• Spring constant


  a measure of how easy it is to stretch or compress a spring; calculated as: force / extension
• Pivot


  the point around which an object turns
• Moment


  a measure of the turning effect of a force that causes an object to rotate about a pivot point, calculated by multiplying force by distance
• Lever


  a rigid bar set on a pivot, used to transfer a force to a load
• Gear


  a wheel with teeth that engages with another wheel with teeth, or with a rack, in order to change the speed or direction of transmitted motion
• Fluid


  a substance, such as a liquid or a gas, which can flow; has no fixed shape
• Normal


  at right-angles to / perpendicular to
• Pressure


  the force exerted on a surface, e.g. by a gas on the walls of a container
• Atmoshpere


  the gaseous envelope surrounding the Earth or another body in space
• Altitude


  the vertical height of an object above sea level
• Dense


  having a high density (mass per volume)
• Upthrust


  an upward push; the upwards force exerted by a fluid on an object in / partially in the fluid
• Displace


  to cause a quantity of liquid, usually water, to move from its usual place
• Distance


  a scalar quantity that provides a measure of how far an object has moved (without taking into account direction)
• Displacement


  a vector quantity that describes how far and in what direction an object has travelled from its origin in a straight line
• Speed


  a scalar measure of the distance travelled by an object in a unit of time, measured in metres per second (m/s)
• Velocity


  a vector quantity that provides a measure for the speed of an object in a given direction
• Accelerating


  the rate of change of velocity, measured in metres per second squared (m/s2 )
• Inertia


  the tendency of a body to stay at rest or in uniform motion unless acted upon by an external force
• Acceleration


  the rate of change of velocity, measured in metres per second squared (m/s2 )
• Gradient


  a measure of the steepness of a sloping line; the ratio of the change in vertical distance over the change in horizontal distance
• Proportional


  describes two variables that are related by a constant ratio
• Inversely proportional


  a relationship between two variables, where one variable increases and the other decreases
• Inertia


  the tendency of a body to stay at rest or in uniform motion unless acted upon by an external force