forces

Question 1

define tension

Answer 1

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

Question 2

define compression

Answer 2

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

Question 3

define friction

Answer 3

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

Question 4

define fluid

Answer 4

a substance that can flow, including liquids or gases

Question 5

define lift

Answer 5

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

Question 6

define normal contact force

Answer 6

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

Question 7

define upthrust

Answer 7

force acting on an object submerged or partially submerged in fluids

Question 8

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

Answer 8

Question 9

What is the definition of one Newton?

Answer 9

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

Question 10

Define Weight

Answer 10

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

Question 11

What is the centre of mass?

Answer 11

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

Question 12

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

Answer 12

Centre of mass is not dependant on the gravitational field.

Question 13

What is the centre of gravity?

Answer 13

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

Question 14

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

Answer 14

When there is a uniform gravitational field

Question 15

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

Answer 15

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

Question 16

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Question 17

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Question 18

what are the factors affecting drag?

Answer 18

• speed
• cross sectional area
• density of fluid

Question 19

what factors affect air resistance?

Answer 19

• cross sectional area
• altitude
• temperature/humididty

Question 20

what is terminal velocity?

Answer 20

when there is a zero resultant force

Question 21

how does mass affect terminal velocity?

Answer 21

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

Question 22

what is a moment?

Answer 22

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

Question 23

what is the principle of moments?

Answer 23

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

Question 24

what is a couple?

Answer 24

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

Question 25

what is a torque?

Answer 25

* 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

Question 26

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Question 27

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Question 28

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Question 29

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Question 30

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Question 31

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Question 32

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Question 33

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

Answer 33

A closed shape (triangle)

Question 34

What is a support force?

Answer 34

* 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

Question 35

What happens when there are two support forces?

Answer 35

* 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

Question 36

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

Answer 36

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

Question 37

What is the principle of moments?

Answer 37

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

Question 39

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Question 40

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Question 41

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Question 42

How is the resultant vector drawn?

Answer 42

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

Question 43

What is the value of the resultant vector in equilibrium?

Answer 43

0

Question 44

what is upthrust?

Answer 44

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

Question 45

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

Answer 45

* **volume**: can change * mass: cannot change

Question 46

what is the volume of fluid displaced?

Answer 46

the volume of the body submerged in the fluid

Question 47

what is archimedes principle?

Answer 47

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.

Question 48

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

Answer 48

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

Question 49

what is work done?

Answer 49

force x distance moved in the direction of the force

Question 50

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..

Answer 50

Question 51

define the joule

Answer 51

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

Question 52

What is kinetic energy ?

Answer 52

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

Question 53

What is the derivation of the kinetic energy formula?

Answer 53

Question 54

what does the work done on an object equal? | in tern of kinetic enrgy

Answer 54

the change kinetic energy

Question 55

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

Answer 55

a) 1000 b) 3000 (1000+2000)

Question 56

what is gravitational potential energy?

Answer 56

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

Question 57

what is the work energie principle?

Answer 57

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

Question 58

what is the mechanical power equation? | and derivation

Answer 58

Question 59

what is power?

Answer 59

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)

Question 60

what is efficency?

Answer 60

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