5: Forces

Question 1

Acceleration:

Answer 1

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

Question 2

Atmosphere:

Answer 2

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

Question 3

Braking Distance:

Answer 3

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.

Question 4

Centre of Mass:

Answer 4

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

Question 5

Changes of Momentum:

Answer 5

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

Question 6

Conservation of Momentum:

Answer 6

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

Question 7

Contact Forces:

Answer 7

A force that occurs when objects are physically touching.

Question 8

Displacement:

Answer 8

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.

Question 9

Distance:

Answer 9

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

Question 10

Elastic Deformation:

Answer 10

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

Question 11

Elastic Limit:

Answer 11

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

Question 12

Elastic Potential Energy:

Answer 12

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.

Question 13

Equilibrium:

Answer 13

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

Question 14

Floating:

Answer 14

An object will float 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.

Question 15

Fluid:

Answer 15

A liquid or gas.

Question 16

Forces:

Answer 16

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

Question 17

Inertia:

Answer 17

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

Question 18

Inertial Mass:

Answer 18

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

Question 19

Limit of Proportionality:

Answer 19

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

Question 20

Moment:

Answer 20

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.

Question 21

Momentum:

Answer 21

The product of an object’s mass and velocity.

Question 22

Newtonmeter:

Answer 22

A calibrated spring-balance used to measure weight.

Question 23

Newton’s First Law:

Answer 23

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.

Question 24

Newton’s Second Law:

Answer 24

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

Question 25

Newton’s Third Law:

Answer 25

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

Question 26

Non-Contact Forces:

Answer 26

A force that occurs when objects are physically separated.

Question 27

Plastic Deformation:

Answer 27

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

Question 28

Pressure in a Column:

Answer 28

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.

Question 29

Resolution of Forces:

Answer 29

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

Question 30

Resultant Force:

Answer 30

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

Question 31

Resultant Moment:

Answer 31

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

Question 32

Scalar Quantities:

Answer 32

Quantities that only have a magnitude, not a direction.

Question 33

Sinking:

Answer 33

An object will sink 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.

Question 34

Speed:

Answer 34

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

Question 35

Spring Constant:

Answer 35

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

Question 36

Stopping Distance:

Answer 36

The sum of the thinking and braking distances.

Question 37

Thinking Distance:

Answer 37

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.

Question 38

Upthrust:

Answer 38

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

Question 39

Vector Quantities:

Answer 39

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.

Question 40

Velocity:

Answer 40

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

Question 41

Weight:

Answer 41

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.

Question 42

Work Done:

Answer 42

Work is done on an object 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.