AS unit 1 Definitons

Question 1

Quantity

Answer 1

In S.I. a quantity is represented by a number  a unit,

Question 2

Scalar

Answer 2

A scalar is a quantity that has magnitude only.

Question 3

Vector

Answer 3

A vector is a quantity that has magnitude and direction.

Question 4

resolving a vector

Answer 4

This means finding vectors (the so-called components)
in these directions, which add together vectorially to
make the original vector, and so, together, are
equivalent to this vector.

Question 5

density

Answer 5

density=mass/volume

Question 6

moment

Answer 6

The moment (or torque) of a force about a point is
defined as the force x the perpendicular distance from
the point to the line of action of the force,
i.e. moment = Fxd
Unit: Nm

Question 7

principle of moment

Answer 7

For a system to be in equilibrium, anticlockwise
moments about a point = clockwise moments about
the same point.

Question 8

centre of gravity

Answer 8

is the single point within a body at which the entire weight of the body may be considered to act.

Question 9

displacement

Answer 9

The displacement of a point B from a point A is the shortest distance from A to B, together with the
direction. Unit: m

Question 10

mean speed

Answer 10

total distance travelled/ total time taken

Question 11

instantaneous speed

Answer 11

Instantaneous speed = rate of change of distance

Question 12

mean velocity

Answer 12

total displacement/ total time taken

Question 13

instantaneous velocity

Answer 13

The velocity of a body is the rate of change of

displacement. Unit: ms^-1

Question 14

mean acceleration

Answer 14

change in velocity/time taken

Question 15

instantaneous acceleration

Answer 15

The instantaneous acceleration of a body is its rate of

change of velocity. ms^-2

Question 16

terminal velocity

Answer 16

velocity is the constant, maximum velocity of an object when the resistive forces on it are equal and opposite to the ‘accelerating’ force

Question 17

force

Answer 17

A force on a body is a push or a pull acting on the body from some external body. Unit: N

Question 18

newton’s 3rd law

Answer 18

If a body A exerts a force on a body B, then B exerts an equal and opposite force on A.

Question 19

momentum

Answer 19

momentum of an object is its mass multiplied by its velocity. (p = mv). It is a vector.

Question 20

newton’s 2nd law

Answer 20

rate of change of momentum of an object is
proportional to the resultant force acting on it, and
takes place in the direction of that force.

Question 21

principle of conservation of momentum

Answer 21

The vector sum of the momenta of bodies in a system
stays constant even if forces act between the bodies,
provided there is no external resultant force.

Question 22

elastic collision

Answer 22

A collision in which there is no change in total kinetic energy.

Question 23

inelastic collision

Answer 23

A collision in which kinetic energy is lost.

Question 24

work

Answer 24

magnitude of the force and the distance moved in the direction of the force.( W.D. = Fxcos θ )
Unit: J

Question 25

elastic potential energy

Answer 25

This is the energy possessed by an object when it has been deformed due to forces acting on it. Eelastic = 1⁄2 Fx or 1⁄2 kx^2 Unit: J

Question 26

energy

Answer 26

The energy of a body or system is the amount of work it can do. Unit: J

Question 27

power

Answer 27

This is the work done per second, or energy | transferred per second. UNit: W or Js^-1

Question 28

hooke's law

Answer 28

tension in a spring or wire is proportional to its extension from its natural length, provided the extension is not too great.

Question 29

spring constant

Answer 29

the force per unit extension.

Question 30

stress

Answer 30

Stress is the force per unit cross-sectional area when | equal opposing forces act on a body. Unit Pa or N m^-2

Question 31

strain

Answer 31

Strain is defined as the extension per unit length due to an applied stress. Unit: none

Question 32

young modulus

Answer 32

Young modulus E=tensile stress/tensile strain Unit: Pa

Question 33

crystal

Answer 33

Solid in which atoms are arranged in a regular array. | There is a long range order within crystal structures.

Question 34

crystalline solid

Answer 34

Solid consisting of a crystal, or of many crystals, usually arranged randomly. The latter is strictly a polycrystalline solid. Metals are polycrystalline.

Question 35

amorphous solid

Answer 35

would have atoms arranged quite randomly.

Question 36

reaction time

Answer 36

time between incident seen and applying break

Question 37

thinking distance

Answer 37

distance travelled during reaction time

Question 38

breaking time

Answer 38

time which break is applied

Question 39

breaking distance

Answer 39

distance travelled during breaking time

Question 40

stopping distance

Answer 40

breaking distance + thinking distance

Question 41

area under unloading curve

Answer 41

work done by rubber band

Question 42

area under loading curve

Answer 42

work done in stretching rubber

Question 43

black body

Answer 43

absorbs all em radiation

Question 44

elastic deformation

Answer 44

returns after being stretched

Question 45

plastic deformation

Answer 45

never returns

Question 46

Brittle

Answer 46

breaks after elastic limit, strong under compression

Question 47

elastic limit

Answer 47

elastic deformation becomes plastic deformation

Question 48

limit of proportionality

Answer 48

beyond this point stress is no longer proportional to strain