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Flashcards in Mechanics Definitions Deck (73)
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1

Any quantity which has both magnitude and direction is a

vector

2

Any quantity which has magnitude only is a

scaler

3

Parallelogram Law states: if two vectors are represented by two adjacent sides ab and ad of a parallelogram abcd then

the diagonal ac represents their resultant

4

a _____ has no components at right angles to itself

vector

5

_______ is the distance of a body, in a given direction, from a fixed point

displacement

6

speed in a given direction =

velocity

7

the rate of change of velocity =

acceleration

8

equations of motion =
V=_+_ _
s=_ _+1/2_ _^-
V^2= _^- + _ _ _

V=u + at
s= ut +1/2at^2
v^2= U^2 + 2as

9

a body has acceleration if it is either its _____ or its _____ is changing

speed or direction

10

ignoring air resistance/ in a vacuum, the acceleration of a falling body due to _____ is always the same

gravity

11

gravity always acts _____ towards ____ ____ __ ___ ____

downwards towards the centre of the earth

12

a body at its highest point has zero _____ but not zero ______

velocity but not acceleration
//acceleration due to gravity still operates

13

Give an example of a scaler quantity

distance
time
mass

14

Give an example of a vector quantity

velocity
force

15

anything which changes , or tends to change, the motion of a body in magnitude or direction =

a force

16

an unbalanced force causes

motion

17

the force with which the earth attracts a body is called the

weight of the body

18

the mass of a body is

the amount of matter in it

19

the product of mass and velocity of a body=

momentum

20

Newtons first law motion

a body remains at rest or moving with uniform velocity unless an unbalanced force acts on it

21

Newtons second law motion

the rate of change of momentum is proportional to the force acting upon it AND takes place in the direction of said force

22

Newtons third law motion

to every action there is an equal and opposite reaction.
//Action and reaction never happen on the same body//

23

equation for force

force = mass x acceleration

24

equation for weight

weight = mass x g

25

A newton is the force which gives ....

an acceleration of 1ms/2 to a mass of 1kg

26

the principle of conservation of momentum states

if no external force acts on a system of colliding bodies the total momentum of the bodies remains constant

27

impulse= change in momentum =

force x time
or
Ft = mv - mu

28

centre of gravity

the point at which the whole weight of the body appears to act is called its centre of gravity

29

the principle of stable design is to have

a low centre of gravity and a wide base

30

a lever is

a rigid body which is free to rotate about a fixed point called the fulcrum

31

the moment of a force about a point is

force x the perpendicular distance from the point to the line of action of the force

32

the principle of moments states

that when a body is in equilibrium the sum of the clockwise moments about any point is equal to the sum of the anticlockwise moments about that point

33

the two conditions for equilibrium are

1. the principle of momentum must apply
2. the vector sum of the forces in any direction is zero

34

the moment of a couple is the product of

one force x the perpendicular distance between them

35

work =

force x distance (moved in the direction of the force)

36

a joule is the work done

when a force of one newton moves its point of application 1m

37

potential energy is

is energy due to position or mechanical condition

38

equation for potential energy

Ep = mgh

39

Kinetic energy is

energy due to motion

40

equation for kinetic energy

Ek = 1/2 mv^2

41

the law of conservation states that

energy can neither be created nor destroyed; it simply changes from one form to another

42

power is the amount

of work done per second

43

1 watt =

1 joule s^-1

44

friction is a force which

opposes relative motion between two bodies in contact

45

lubricants

reduce friction

46

viscosity is

resistance to flow in fluids

47

a sphere falling through a fluid has three forces acting on it. List these three forces

1. Its weight W acting downwards
2. An upthrust U due to displaces liquid
3. A frictional force F acting upwards
//W and U are constant. As the sphere begins to fall, it accelerates but, as its velocity increases, F also increases until U + F = W and the net force acting on the sphere is zero.
It now continues to fall with a uniform/ constant velocity known as terminal velocity

48

the mass of unit volume of a substance is called its

density

49

pressure=

force per unit area

50

the unit of pressure is the

pascal
1 Pa = 1Nm^2

51

pressure in a fluid depends on three things;
(give equation)

depth, density and acceleration due to gravity
P = pgh

52

Archimedes' Principle:

A body partly or wholly immersed in a fluid experiences a upthrust equal to the weight of the fluid displaced

53

law of flotation:

A floating body displaces its own weight of fluid

54

the angular velocity is the rate of change of

angle in radians per second,
ω = θ/t

55

The periodic time equation

T= 2π/ω

56

Linear Velocity equation

arc/t = rθ/t = rω
v = rω

57

Acceleration towards the centre of a circle equation

a = rω^2 or a = v^2/r

58

the force necessary to keep a body moving in a circle is a

centripetal force acting towards the centre of the circle.
F = mrω^2
or F = mv^2/r

59

The Law of gravitation;

the force of attraction between any two bodies is proportional to their masses and inversely proportional to the square of the distance between them

f ∝ (M1 M2)/d^2 ⇒ F = (GM1M2)/d^2
mg =GmM/d^2 ⇒ g/G = M/ d^2 or g = GM/d^2

60

Give Kepler's Three laws of planetary motion

1. The Planets move in elliptical orbits round the sun as one focus.
2. The line joining the sun and the planet sweeps out equal areas in equal time intervals
3. The square of the periodic time of a planet is proportional to the cube of its mean distance from the sun. // GmM/r^2 = mrω^2 = mr (4π^2/T^2) ⇒ T^2 = 4π^2r^2/GM//

61

Give Kepler's Third Law mathematically

GmM/r^2 = mrω^2 = mr (4π^2/T^2) ⇒ T^2 = 4π^2r^2/GM

62

For the signal of a satellite to be transmitted from earth to said satellite and back the satellite must always be above the same point on the earth. i.e it mus have the same period as the earth - 24 hours. The satellite is said to be

geostationary or parking orbit

63

Hooke's Law;

Provided a spring is not extended beyond its elastic limit, the extension is proportional to its load.

64

give the mathematical definition of simple harmonic motion ( S.H.M )

a = -ω^2s
// the minus indicates that the body begins to retard as it passes through 0, the centre of its motion

65

when a particle is undergoing S.H.M its acceleration is

maximum when its displacement is maximum

66

Give an example where a body has acceleration but zero velocity

a body that has been thrown vertically upwards and is at its greatest height.

67

When does a body travelling at constant speed have an acceleration?

when it is changing direction

68

Why is it easier to turn a nut using a longer spanner rather than a shorter one?

The distance from the effort to the fulcrum is greater, giving a greater turning effect.

69

State the law of flotation

a floating body displaces its own weight of fluid.

70

A container contains 5kg of water. if the area of the base of the container in 0.5m ^2, what is the pressure on the base?

P = F/A = (5 x 9.8)/0.5 = 98 Pa

71

What is the relationship between the acceleration due to gravity, g and the distance from the centre of the earth?

g ∝ 1/d^2

72

A particle travels at constant speed of 10ms-1 in a circle of radius 2m. What is its angular velocity?

v = rω ⇒ ω = v/r = 10/2 =5 radians per second

73

The moon orbits the earth. What is the relationship between the period of the moon and the radius of its orbit?

T^2 ∝ R^3 (Kepler's third Law)