Flashcards in Mechanics -Terms and definitions Deck (100):

28

## Newton's First Law of Motion

###
If all the forces acting upon an object are balanced, then the object will either stay stationary or travel at a constant speed/velocity.

d=vt

(Acceleration = 0)

If the forces acting upon an object are NOT balanced, then the object will have an acceleration. The direction of the acceleration will be the same as the net force.

a=F/m or F=ma

2

## Newton's Second Law of Motion

###
If acceleration and velocity are in the same direction, the object is accelerating.

If acceleration and velocity are in opposite directions, the object is decelerating.

Where there is an acceleration we use kinematic equations.

20

## Kinematic Equations

###
Vf=Vi+at

d=Vit+1/2at^2

Vf^2=Vi^2+2ad

d=((Vi+Vf)/2)t

Vi = initial velocity (m/s)

Vf = final velocity (m/s)

t = time (s)

a = acceleration (ms^-2)

d = distance (m)

27

## Newton's Third Law of Motion

### Every acting force will have an equal and opposite reaction force.

1

## Gravitational Acceleration

### 9.8m/s/s

22

## Conservation of Energy

###
Energy cannot be created or destroyed

In a system that does not undergo any force from outside the system, the amount of energy is constant, irrespective of its changes in form.

25

## Verticle Motion under Gravity

### When an object is under free-fall, provided air resistance can be ignored, its acceleration is due to gravity.

18

## Projectile def

### A projectile is any object that moves through the air without its own source of power, only under the influence of gravity (air resistance is ignored).

7

## Projectile motion horizontal

### In the horizontal direction, there is no force acting on the object, so the horizontal velocity will stay the same. (No acceleration).

15

## Projectile motion vertical

### In the vertical direction, the only force that is acting is gravity going down. It is under constant acceleration at 9.8m/s/s

10

## Torque

###
Def: Torque is the turning effect of a force around a pivot point.

Torque is sometimes called 'moment', or 'moment of force'.

symbol: T

24

## Torque Calculations

###
T=Fd

T = Torque = Newtons per meter = N.m

F = Force = Newtons = N

d = perpendicular distance (from pivot pt.) = meters = m

Tac=Tc

Tac = Sum of Torque anticlockwise

Tc = Sum of Torque clockwise

31

## Momentum equations

###
P=mv

P = momentum = kg.m/s

m = mass = kg

v = velocity = m/s

Ptotal-> = Pa-> + Pb->

9

## Equilibrium

###
All forces are balanced, no linear acceleration.

Clockwise torque equals to anticlockwise torque, no angular acceleration.

14

## Circular Motion

###
"Newton's first law states that a body will continue at a constant velocity in a straight line unless it is acted on by an external force. The velocity of the spinning object is constantly changing so there must be an external force acting upon it -the centripetal force. Remove the centripetal force and the object flies off at a tangent."

An object rotates around a fixed point with a constant speed and radius.

The direction of the velocity is TANGENTAL (In tangent to the circle)

Even though the SPEED of the object does not change, the direction is constantly changing thus the velocity is constantly changing.

23

## Fc

### Centripetal force

16

## ac

### centripetal acceleration

4

## Circular motion equations (5)

###
Fc=mac

Fc = centripetal force = Newtons = N

m = mass = kg

ac = centripetal acceleration = m/s/s

v=(2πr)/T =2πrF

v = velocity = m/s

π = pie

r = radius

T = period = unit: S

F = frequency = unit: S^-1 or Hertz (Hz)

Fc=(mv^2)/r

c=2πr

c = circumfrence

π = pie

r = radius

ac=(v^2)/r

17

## Period (T)

###
def: The time that it takes for one revolution (one circle) to occur.

Unit: S

29

## Frequency (F)

###
def: The number of revolutions that can happen in 1 second.

Unit: S^-1 or Hertz (Hz)

8

## Rounding

###
To the least accurate amount of significant figures that is given in the question.

Because the end result's accuracy can't be more accurate than the data given itself.

(Round at the end of the question only)

11

## Momentum

###
The quantity of motion of a moving body, measured as a product of its mass and velocity.

Used in EXPLOSIONs and COLLISIONs.

"Moving objects resist being stopped, a quality which we call their inertia. We experience a force when struck by a moving object created by a change in momentum."

Momentum is a vector quantity, it has both size and direction. The direction of momentum is the same as the velocity.

26

## Kinetic Energy

###
Is the energy an object has because of its movement. As an object speeds up it gains kinetic energy, as it slows down it loses it.

Ek=(1/2)mv^2

30

## Gravitational Energy

###
When an object is able to gain kinetic energy in the future on account of its position, being raised above the ground.

ΔEp=mgΔh

6

## Power

###
The rate at which energy is transformed (how fast it's transformed).

P=W/t or P=ΔE/t

P = Power -J/s or Watts (W)

W = Work (J)

ΔE = change in energy (J)

t = time (s)

32

## Work

###
If a force acting on an object has moved the object in the direction of the force for a distance, then we say the force has DONE WORK.

Work done = energy transformed

thus

when energy is transformed, there must be a force doing work.

W=Fd

19

## Impulse

###
Change of momentum is caused by a force over a period of time.

ΔP->=Ft

ΔP = kgm/s (the arrow shows the direction of the net impulse).

F = N

t = s

13

## Conservation of Momentum

###
The momentum of a system stays the same if there's no external force acting on it.

This is used in collisions and explosions.

3

## Elastic and Inelastic Collisions

###
During a collision, if there is NO loss of kinetic energy, we call it ELASTIC collision.

During a collision, if there IS loss of kinetic energy, we call it INELASTIC collision.

(There will always be some lost due to friction, but if it's a not much then it's inelastic)

Ek=(1/2)mv^2

5

## Energy Equations (5)

###
P=W/t

W=F/d

Ek=(1/2)mv^2

W=Pt

Ep=mgΔh

21

## Spring Constant

###
Represents the stiffness of the spring (the bigger the spring constant the stiffer the spring)

F=kx or F=-kx

F = Force (N)

k = Spring constant (N/m)

x = Extension (m)

(-) = Restoring force in the spring -essentially the force opposing the extension (downwards) force. Don't often need to use.

12

## Elastical Potential Energy

###
Stretched out string, once you let it go it will contract similar to dropping a ball w gravitational Ep.

Ep=(1/2)kx^2

Ep = Elastic Potential Energy (J)

k = spring constant (N/m)

x = extension (m)

33

## Accelerate vs acceleration

###
Accelerate: When something changes its velocity

Acceleration: The rate of change of velocity of a moving object. Can result from a change in speed and/or a change in direction

34

## Acceleration due to gravity

###
On surface of earth, value is 9.8ms^-2

Increases nearer the poles, decreases with altitude and depth inside the earth

35

## Average velocity

### Total displacement divided by the total time taken

36

## Axis

### The imaginary line about which a planet or other object rotates

37

## Balanced forces

### When a number of forces act on a body, and the resultant force is zero

38

## Centripetal force

### Force required to keep an object moving in a circle

39

## Change in momentum

### Momentum after minus momentum before

40

## Change in velocity

### Velocity after minus velocity before

41

## Circular motion

### The motion of a body along a circular path

42

## Circular orbit

### An orbit that is circular

43

## Collision

### Objects hitting eachother

44

## Combined mass

### Sum of masses involved

45

## Conservation of energy

### When energy is transformed from one type of energy into another, the total energy before and after are always the same.

46

## Conservation of mass

### Mass, including single atoms, is neither created or destroyed in a chemical reaction (not measurably anyway!)

47

## Conservation of momentum

### The total momentum of a group of a closed system remains constant in the absence of external forces

48

## Constant speed

### Speed that stays the same

49

## Deceleration

### Negative acceleration

50

## Displacement

### The change in the position of an object in a particular direction

51

## Distance

### The actual length of the path traveled by a body irrespective of the direction is called the distance traveled

52

## Equations of motion

### Set of formulas used to describe motion mathematically

53

## Force

### Forces change the state of rest or of uniform motion, the direction of motion, or the shape and size of a body

54

## Force of gravitation

### The force with which two objects attract eachother because of their masses

55

## Free fall

### The motion of a body towards the earth when no other force except weight acts on it.

56

## Friction

### The force that resists the motion of one surface relative to another with which it is in contact

57

## Gravitational constant G

### The universal gravitational constant G which appears in the equation for Newton's law of gravitation

58

## Gravity

### Forces of attraction between two objects due to their mass

59

## Horizontal circle

### A circle that involves no gain or loss in gravitational potential energy

60

## Impulse

### Change in momentum caused by an external force

61

## Inelastic collision

### Collision where kinetic energy is not conserved (some energy is converted to sound or heat etc.)

62

## Inertia

### The property of matter that causes it to resist any change in its state of rest or of uniform motion

63

## Kinetic energy

### Energy possessed by a body by the virtue of its motion

64

## Mass

### The quantity of matter contained in a body it remains the same everywhere

65

## Matter

### Anything that occupies space and has mass

66

## Momentum

### The product of a body's mass and velocity

67

## Motion

### Manner of how a body moves

68

## Net force

### The resulting force after all forces have been added using vector

69

## Newton

### A unit of force defined as 1 Newton force is needed to accelerate a 1kg mass 1 ms^-2

70

## Newton's first law of motion

### A body continues in a state of rest or of uniform motion in a straight line unless it is acted upon by an external force

71

## Newton's law of gravitation

### Force between two particles is proportional to their masses and inversely proportional to the square of the distance between them

72

## Non Uniform Acceleration

### When the velocity of a body increases by unequal intervals of time

73

## Non Uniform Speed

### When a body travels unequal distances in equal intervals of time

74

## Non Uniform Velocity

###
Covers unequal distances in equal intervals of time in one direction

Covers equal distances in equal intervals but changes direction

75

## Origin

### Initial position of an object

76

## Oscillatory motion

### The to and fro motion of a body about its mean position

77

## Pendulum

### A mass (called "Bob") tied to a piece of string

78

## Period

### For a particular vibration, the time for one complete oscillation

79

## Pivot

### Point upon which an object turns or rotates

80

## Potential Energy

### The energy of a body due to its height or the energy of a body due to its shape

81

## Projectile

### An object thrown into space either horizontally and under the action of gravity

82

## Radius

### Distance from centre of circle to edge

83

## Range

### The horizontal distance traveled by a projectile

84

## Rectilinear Motion

### The motion of a body in a straight line is called rectilinear motion

85

## Retardation

### Negative acceleration is called retardation. In retardation the velocity of a body decreases over time

86

## Revolution

### One full circle 2π

87

## Speed

### The distance traveled by a body in one unit of time is called its speed

88

## Spring Constant

### Force required to extend or compress a spring by one metre

89

## State of motion

### When a body changes its position with respect ot a fixed point

90

## State of Rest

### When a body does not change its position with respect to a fixed point

91

## Tangential velocity

### Velocity in a perpendicular direction to the centripetal force at a given instant

92

## Tension force

### Force in object that opposes them being stretched

93

## Time of flight

### The time taken by a projectile from the moment it is thrown until it touches the ground

94

## Torque

### Turning force (not applied through the centre of mass)

95

## Unbalanced forces

### When a number of forces act on a body and the resultant force is not zero

96

## Uniform circular motion

### The motion of an object in a circular path with uniform speed

97

## Velocity

### Distance traveled by a body in a particular direction per unit time

98

## Vertical circle

### Circular motion where the speed, as well as the direction of the object, is constantly changing

99

## Weight

### The force with which a body is attracted towards the center of the earth

100