Forces: Keywords

acceleration

acceleration

The rate of change of velocity. It can be calculated from the gradient of a velocity-time graph.

atmosphere

The thin layer of air surrounding the Earth, which gets less dense with increasing altitude.

braking distance

The distance a vehicle travels under the braking force. This can be affected by adverse road and weather conditions as well as the condition of the vehicle.

center of mass

The single point through which the weight of the object can be said to act.

changes in momentum

When a force acts on a moving object, or one an object that has the ability to move, this will occur. The force is equal to the rate of - .

conservation of momentum

The total momentum of a system before an event is always equal to the total momentum of the system after the event.

contact force

A force that occurs when objects are physically touching.

displacement

A measure of how far an object moves in a given direction. It is the straight line between the starting and finishing points and is a vector quantity.

distance

A measure of how far an object moves, that does not depend on direction and is therefore a scalar quantity.

elastic deformation

Non-permanent deformation which allows the object to return to its original shape when the deforming forces are removed.

elastic limit

The force beyond which an object will no longer deform elastically, and will instead deform plastically.

elastic potential energy

The energy stored in a spring when it is stretched or compressed, due to the work done on the spring by the deforming force. It is equal to the work done as long as the object does not plastically deform.

equilibrium

An object is in this if the resultant force and resultant moment are both equal to zero.

floating

An object will - if the volume of liquid it displaces has a greater weight than that of the object itself. The upthrust acting on the object is greater than its weight.

fluid

A liquid or gas.

forces

A push or pull that an object experiences due to the interaction with another object. Force is a vector quantity.

inertia

The tendency of an object to remain in its same state of uniform motion or rest.

inertial mass

A measure of how hard it is to change an object’s velocity. It is defined as the ratio of force over acceleration.

limit of proportionality

The point beyond which the extension of an elastic object is no longer directly proportional to the force applied to it.

moment

The turning effect of a force, equal to the product of the magnitude of the force and the perpendicular distance from the pivot to the line of action of the force.

momentum

The product of an object’s mass and velocity.

newton meter

A calibrated spring-balance used to measure weight.

Newton’s first law

If a stationary object’s resultant force is zero, the object will remain stationary. If a moving object’s resultant force is zero, the object will continue to move at the same speed, and in the same direction.

Newton’s second law

An object’s acceleration is directly proportional to the force applied to it, and inversely proportional to its mass.

Newton’s third law

The forces that two objects exert on each other when they interact are equal and opposite.

non-contact forces

A force that occurs when objects are physically separated.

plastic deformation

Permanent deformation which means the object will no longer return to its original shape when the deforming forces are removed.

pressure in a column

The pressure in a column of liquid is equal to the product of the liquid’s density, the height of the column and the gravitational field strength.

resolution of forces

All forces can be resolved into two perpendicular components that have the same effect as the single force.

resultant orce

The single force that can replace all the individual forces acting on an object, and have the same effect.

resultant moment

The single moment that has the same effect as the sum of all the other clockwise and anticlockwise moments acting on an object.

scalar quantities

Quantities that only have a magnitude, not a direction.

sinking

An object will - if the volume of liquid it displaces has a lower weight than that of the object itself. The upthrust acting on the object is lower than its weight and so there is a resultant downwards force

speed

A scalar quantity that is a measure of the rate of increase of distance.

spring constant

A measure of a spring’s stiffness, which is the constant of proportionality for a spring’s extension. The higher this is, the smaller the extension is for a given force.

stopping distance

The sum of the thinking and braking distances.

thinking distance

The distance a vehicle travels during the driver’s reaction time. Typical human reaction times are in the range of 0.2-0.9 seconds. This reaction time may be affected by tiredness, drugs or alcohol.

upthrust

The upward force acting on an object in a fluid, due to it experiencing a greater pressure below it than above it.

vector quantities

Quantities that have both a magnitude and direction. They are represented by an arrow, with the length representing the magnitude and the arrowhead representing the direction.

velocity

A vector quantity that is a measure of the rate of change of displacement. It is the speed in a given direction.

weight

The force acting on an object due to gravity. It is equal to the product of the object’s mass and the gravitational field strength at its location.

work done

When a force causes it to move through a distance. It is directly proportional to the distance travelled and the magnitude of the force in the direction of motion.