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forces Flashcards

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1
Q

define tension

A

A force experienced by a cable, rope , or strung when pulled, hung, rotated or supported.

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2
Q

define compression

A

a decrease in the length of an object when a compressive force is exerted on it

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3
Q

define friction

A

a resitive force on an object that is caused by two surfaces being in contact, acting in the opposite direction to motion

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4
Q

define fluid

A

a substance that can flow, including liquids or gases

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5
Q

define lift

A

a force caused by the flow of a fluid around an object, which acts perpendicular to the fluid flow

most often in the upwards direction

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6
Q

define normal contact force

A

a reaction force exerted by a surface on an object which acts perpendicular to the surface

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7
Q

define upthrust

A

force acting on an object submerged or partially submerged in fluids

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8
Q

What is the special equation from Newton’s 2nd Law?

A
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9
Q

What is the definition of one Newton?

A

The force required to accelerate the mass of 1kg by 1ms^-2 in the direction of the force

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10
Q

Define Weight

A

The gravitational force acting on an object, proportional to its mass. On Earth W=mg

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11
Q

What is the centre of mass?

A

The point through which any externally applied force produces straight line motion but no rotation

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12
Q

What is the difference between the centre of mass and then centre of gravity?

A

Centre of mass is not dependant on the gravitational field.

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13
Q

What is the centre of gravity?

A

An imaginary point where the entire weight of an object appear to act

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14
Q

When do the centre of gravity and centre of mass act in the same place?

A

When there is a uniform gravitational field

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15
Q

How do you find the centre of mass for a realistic body?

A
  1. suspend the body from a position near it’s edge
  2. allowing it to come to rest
  3. drawing a line vertically down, use a plumb line to guide
  4. suspend it from another point and repeat
  5. Centre of Mass lays where the lines intersect

if body comes to rest—>weight acts through centre of mass = 0 momentum

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16
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17
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18
Q

what are the factors affecting drag?

A
  • speed
  • cross sectional area
  • density of fluid
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19
Q

what factors affect air resistance?

A
  • cross sectional area
  • altitude
  • temperature/humididty
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20
Q

what is terminal velocity?

A

when there is a zero resultant force

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21
Q

how does mass affect terminal velocity?

A

the higher the mass, the
higher the terminal velocity, because the object with a heavier mass will reach eqilibrium at a higher terminal velocity

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22
Q

what is a moment?

A
  • the turning effect of a force
  • causing objects to rotate about a pivot point
  • force times perpendicular distance from pivot to line of action
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23
Q

what is the principle of moments?

A

when in equlibrium, the sum of clockwise moments= the sum of anti clockwise moments

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24
Q

what is a couple?

A

a pair of equal and opposite co-planar forces that act to produce a rotation only, no translational force

distance between the forces must be perpendicular

produce a Resultant force of 0 but a resultant moment

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25
Q

what is a torque?

A
  • the moment of a couple
  • unlike moments doesn’t depend of a pivot point
  • force(one of the forces) * perpendicular distance between the lines of action of the forces
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28
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29
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30
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31
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32
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33
Q

How do you show in a free body diagram that there is equilibrium and a zero resultant force?

A

A closed shape (triangle)

34
Q

What is a support force?

A
  • acts when a body is in contact with a surface
  • when bodies are balanved horizonatlly, the support force always acts upwards
  • for bodies in equilibrium the support force up must equal all the forces acting down

force acts on the pivot so no momentum

35
Q

What happens when there are two support forces?

A
  • taking moments about one pivot means you must take into account the moment of the support force from the second pivot
  • value of support force is determined where the centre of mass lies
36
Q

what does it mean for a body to be in equilibrium?

A

the net force and net moment acting on a body are zero

37
Q

What is the principle of moments?

A

for a body in rotational equilibrium, the sum of anti-clockwise moments is equal to the sum of clockwise moments
* Σ M⟲= Σ M⟳

38
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39
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40
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41
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42
Q

How is the resultant vector drawn?

A

From unconnected tail of first vector the the unconnected tip of the last vector

43
Q

What is the value of the resultant vector in equilibrium?

A

0

44
Q

what is upthrust?

A
  • the weight of that water pushing on the body
  • = weight of fluid displaced
  • caused due to pressure difference between top and bottom of body
45
Q

what factprs of an object can cuase a change in the upthrust experiences?

A
  • volume: can change
  • mass: cannot change
46
Q

what is the volume of fluid displaced?

A

the volume of the body submerged in the fluid

47
Q

what is archimedes principle?

A

the upthrust exerted on a body immersed in a fluid whether fully or partially submerged is equal to the weight of the fluid that body displaces.

48
Q

how does archemidies principle explain why larger volume objects have a larger upthrust?

A
  1. larger volume objects displace more of the fluid
  2. the weight of the fluid displaced increases
  3. (archemidies principle) more upthrust
49
Q

what is work done?

A

force x distance moved in the direction of the force

50
Q

A person of mass 80kg travels own a zipline at an angle of 7 degress from the horizontal. Calculate the work done on the person by earth’s gravity over a 20m section. Ignore resistive forces..

A
51
Q

define the joule

A

the work done when a constant force of 1N moves it’s point of application 1m in the direction of the force

52
Q

What is kinetic energy ?

A

The energy that a body has when in motion.
Dependant on mass and velocity

53
Q

What is the derivation of the kinetic energy formula?

A
54
Q

what does the work done on an object equal?

in tern of kinetic enrgy

A

the change kinetic energy

55
Q

A toy car is accelerated through a distance of 20m by a motor which imparts a force of 50N on the car. If the car has an initial kinetic energy of 2000 J and the system is otherwise isolated:

  • a)Calculate the work done on the car by the motor
  • b) Calculate the final kinetic energy of the toy car
A

a) 1000
b) 3000 (1000+2000)

56
Q

what is gravitational potential energy?

A

The stored potential energy of an object due to position in a gravitational field, associated with the weight of a body at a given vertical height above the Earth’s surface, EP = mgh

57
Q

what is the work energie principle?

A

The total work done by all the forces acting on a body is equal to the change in kinetic energy of the body

58
Q

what is the mechanical power equation?

and derivation

A
59
Q

what is power?

A

Power is the rate of work done with respect to time or the rate of energy transferred with respect to time

P = W/t where P = power (in Watts), W = work done (in Joules) and t = time (in seconds)

60
Q

what is efficency?

A

Efficiency is the ratio of useful energy transferred over total energy supplied, expressed as a percentage.

Efficiency = (the useful output energy divided by the total input energy) x 100

61
Q
A

Physics (old) (10 decks)

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