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Physics > Forces in Action > Flashcards

Forces in Action Flashcards

(67 cards)

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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
What is the resultant?
The diagonal of the parallelogram that starts at the origin of the two forces
25
What does resolving a force mean?
Finding perpendicular components that have a resultant force that is equal to the force
27
The weight of an object is the ...
.. force acting on the object due to gravity
28
An object at rest in equilibrium is there because ...
.. the resultant force on it is zero
29
What is velocity?
Speed in a given direction
30
What is a vector?
A physical quantity that has a direction as well as a magnitude
31
What is a scalar?
A physical quantity that has a magnitude only and does not have a direction
32
What is deceleration?
The change of velocity per second when an object slows down
33
A motion sensor linked to a computer can be used to ...
.. measure velocity changes
34
The gradient of the line on a velocity-time graph represents ...
.. acceleration
35
A postive gradient on a velocity-time graph represents ...
.. positive acceleration
37
If the resultant force on an object is ...
- 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
A negative gradient on a velocity-time graph represents ...
.. deceleration
39
The area under the line on a velocity-time graph represents ...
.. distance travelled
40
The greater the resultant force on an object ...
.. the greater the object's acceleration
40
The greater the mass of an object ...
.. the smaller its acceleration for a given force
41
What is the terminal velocity of an object?
The velocity it eventually reaches when falling. The weight of the object is then equal to the frictional force on the object
42
When an object is moving at terminal velocity, the resultant force on it is ...
.. zero
43
What forces oppose the driving force of a vehicle?
- friction | - air resistance
44
What does the stopping distance of a vehicle depend on?
- thinking distance | - braking distance
45
What factors affect thinking distance?
- speed of travel | - poor reaction time (under the influence, using a mobile phone)
46
Why can an object be described as elastic?
If it returns to its original shape after removing the force deforming it
47
What is a closed system?
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
When vehicles collide, the force of the impact depends on ...
- mass - change of velocity - length of impact time
50
What factors affect braking distance?
- poor weather conditions - poor car maintainance - poor road conditions
51
What happens when two vehicles collide?
- they exert equal and opposite forces on eachother | - their total momentum is unchanged
52
Cycle helmets and cushioned surfaces ...
.. reduce impact of forces by increasing the impact time
53
Seat belts and air bags ...
.. spread the force across the chest and increase the impact time
54
Side impact bars and crumple zones ...
.. give way an impact and increase the impact time
54
What can conservation of momentum be used for?
To find the speed of a car before impact
55
The extension of a spring is directly proportional to ...
.. the force applied to it
56
Beyond the limit of proportionality ...
.. the extension of a spring is no longer proportional to the applied force
57
The pressure in a liquid increases with ...
.. increasing liquid depth
58
What caused the upthrust on an object in a fluid?
The pressure of the fluid
59
A liquid flows until ...
.. the pressure along the same horizonal level is constant
60
The greater the density of a liquid ...
.. the greater the pressure of the liquid
62
What is the extension of an object?
The difference between the length of the object and its original length
63
Air molecules collide with surfaces and create ...
.. pressure on them
64
Why do objects sink?
If the weight is greater than the upthrust on the object when it is fully immersed
65
Why does atmospheric pressure decrease with higher altitude?
There is less air above a given altitude than there is at a lower altitude.
66
The density of the atmosphere decreases with ...
.. increasing altitude
67
What is the upthrust on an object in a fluid?
An upward force on the object due to the fluid.
67
The pressure at a point in a fluid depends on the ...
- density of the fluid | - the depth of the fluid at that point

Physics (5 decks)

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