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Physics > Forces in Action > Flashcards

Forces in Action Flashcards

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1
Q

What is a vector quantity?

A

A physical quantity which has magnitude and direction

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2
Q

What is a scalar quantity?

A

Something with magnitude but no direction

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3
Q

What can forces do?

A
  • change somethings shape
  • change somethings motion
  • change somethings state of rest
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4
Q

What is force measured in?

A

Newtons (N)

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5
Q

What is a contact force?

A

A force that acts on objects only when the objects touch eachother

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6
Q

When two objects interact they …

A

.. always exert equal and opposite forces on eachother

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7
Q

What is resultant force?

A

A single force that has the same effect as all the forces acting on an object

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8
Q

What is the resultant force if two forces act on an object in the same direction?

A

It is the sum of the two forces

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9
Q

What is the resultant force of an object if two forces are acting in opposite directions?

A

It is the difference of the two forces

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10
Q

What is displacement?

A

Distance in a given direction

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11
Q

What does a free-body force diagram show?

A

The forces acting on the object

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12
Q

What is the moment of a force?

A

A measure of the turning effect of the force on an object

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13
Q

How do you increase the moment of a force?

A

-increase the force
OR
-increase the distance

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14
Q

What is the parallelogram of forces?

A

A scale diagram of two force vectors

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15
Q

What happens if you use a lever as a force multiplier?

A
  • it exerts a greater force than the force applied to the lever by effort
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16
Q

Gears are used to …

A

.. change the moment of a turning effect

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17
Q

How do you draw vector quantities?

A
  • an arrow in the direction of the vector with a length in proportion to the magnitude
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18
Q

How do you resolve a force in two perpendicular directions?

A

Draw a rectangle with adjacent sides along the two directions so the diagonal represents the force vector

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19
Q

Low gear gives a …

A

.. Low speed and high turning effect

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20
Q

High gear gives a …

A

.. high speed and low turning effect

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21
Q

What is the centre of mass of an object?

A

the point where its mass can be thought of as being concentrated

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22
Q

When an object is freely suspended …

A

.. it come to rest with its centre of mass directly below the point of suspension

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22
Q

What is the parallelogram of forces used for?

A

To find the resultant of two forces that do not act along the same line

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23
Q

The direction of the force and the position of the fixed point determines whether the …

A

.. moment acts clockwise or anti-clockwise

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24
Q

What is the resultant?

A

The diagonal of the parallelogram that starts at the origin of the two forces

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25
Q

What does resolving a force mean?

A

Finding perpendicular components that have a resultant force that is equal to the force

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27
Q

The weight of an object is the …

A

.. force acting on the object due to gravity

28
Q

An object at rest in equilibrium is there because …

A

.. the resultant force on it is zero

29
Q

What is velocity?

A

Speed in a given direction

30
Q

What is a vector?

A

A physical quantity that has a direction as well as a magnitude

31
Q

What is a scalar?

A

A physical quantity that has a magnitude only and does not have a direction

32
Q

What is deceleration?

A

The change of velocity per second when an object slows down

33
Q

A motion sensor linked to a computer can be used to …

A

.. measure velocity changes

34
Q

The gradient of the line on a velocity-time graph represents …

A

.. acceleration

35
Q

A postive gradient on a velocity-time graph represents …

A

.. positive acceleration

37
Q

If the resultant force on an object is …

A
  • zero, the object stays at rest or at same speed and direction
  • greater than zero, the speed or direction of the object will change
38
Q

A negative gradient on a velocity-time graph represents …

A

.. deceleration

39
Q

The area under the line on a velocity-time graph represents …

A

.. distance travelled

40
Q

The greater the resultant force on an object …

A

.. the greater the object’s acceleration

40
Q

The greater the mass of an object …

A

.. the smaller its acceleration for a given force

41
Q

What is the terminal velocity of an object?

A

The velocity it eventually reaches when falling. The weight of the object is then equal to the frictional force on the object

42
Q

When an object is moving at terminal velocity, the resultant force on it is …

A

.. zero

43
Q

What forces oppose the driving force of a vehicle?

A
  • friction

- air resistance

44
Q

What does the stopping distance of a vehicle depend on?

A
  • thinking distance

- braking distance

45
Q

What factors affect thinking distance?

A
  • speed of travel

- poor reaction time (under the influence, using a mobile phone)

46
Q

Why can an object be described as elastic?

A

If it returns to its original shape after removing the force deforming it

47
Q

What is a closed system?

A

A system in which the total momentum before an event is the same as the total momentum after an event. This is called conservation of momentum

48
Q

When vehicles collide, the force of the impact depends on …

A
  • mass
  • change of velocity
  • length of impact time
50
Q

What factors affect braking distance?

A
  • poor weather conditions
  • poor car maintainance
  • poor road conditions
51
Q

What happens when two vehicles collide?

A
  • they exert equal and opposite forces on eachother

- their total momentum is unchanged

52
Q

Cycle helmets and cushioned surfaces …

A

.. reduce impact of forces by increasing the impact time

53
Q

Seat belts and air bags …

A

.. spread the force across the chest and increase the impact time

54
Q

Side impact bars and crumple zones …

A

.. give way an impact and increase the impact time

54
Q

What can conservation of momentum be used for?

A

To find the speed of a car before impact

55
Q

The extension of a spring is directly proportional to …

A

.. the force applied to it

56
Q

Beyond the limit of proportionality …

A

.. the extension of a spring is no longer proportional to the applied force

57
Q

The pressure in a liquid increases with …

A

.. increasing liquid depth

58
Q

What caused the upthrust on an object in a fluid?

A

The pressure of the fluid

59
Q

A liquid flows until …

A

.. the pressure along the same horizonal level is constant

60
Q

The greater the density of a liquid …

A

.. the greater the pressure of the liquid

62
Q

What is the extension of an object?

A

The difference between the length of the object and its original length

63
Q

Air molecules collide with surfaces and create …

A

.. pressure on them

64
Q

Why do objects sink?

A

If the weight is greater than the upthrust on the object when it is fully immersed

65
Q

Why does atmospheric pressure decrease with higher altitude?

A

There is less air above a given altitude than there is at a lower altitude.

66
Q

The density of the atmosphere decreases with …

A

.. increasing altitude

67
Q

What is the upthrust on an object in a fluid?

A

An upward force on the object due to the fluid.

67
Q

The pressure at a point in a fluid depends on the …

A
  • density of the fluid

- the depth of the fluid at that point

Physics (5 decks)

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