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Physics > Forces > Flashcards

Forces Flashcards

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1
Q

What can forces do?

A

A force can change the shape of an object or change its state of res or its motion.

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2
Q

What is the unit of force?

A

Newton (N)

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3
Q

When two objects interact, what can we say about the forces acting?

A

When two objects interact, they always exert equal and opposite forces on each other.

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4
Q

What force makes a car move?

A

Driving force.

Sometimes called engine force / motive force

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5
Q

What is driving force due to?

A

It is due to friction between the ground and tyre of each drive wheel.

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6
Q

When does friction act when there is a driving force on the car

A

Friction acts where the tyre is in contact with the ground.

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7
Q

What is a 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 happens if the resultant for on an object is zero?

A

The object remains stationary or moves at constant velocity.

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9
Q

What happens if the resultant for on an object is not zero?

A

The velocity of the object will change.

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10
Q

How do we calculate the resultant force when an object is acted on by two forces acting along the same line?

A

The resultant force is:
•their sum if the forces act in the same direction.
•their difference if the forces act in opposite directions.

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11
Q

What is the equation for the resultant force?

A

Resultant force = mass x acceleration

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12
Q

How does acceleration if an object depend on the size of the resultant force?

A

The bigger the resultant force on an object, the greater its acceleration is.

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13
Q

What effect does the mass of the object have on its acceleration?

A

The greater the mass of an object is, the smaller its acceleration is for a given force.

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14
Q

What happens to the velocity if the resultant force is in the same direction as the velocity?

A

The velocity increases.

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15
Q

What happens to the velocity if the resultant force is in the opposite direction to its velocity?

A

The velocity decreases (decelerates).

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16
Q

What happens to the acceleration if it’s in the same direction as its velocity?

A

The acceleration is positive.

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17
Q

What happens to the acceleration if it’s in the opposite direction to its velocity?

A

The acceleration is negative.

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18
Q

What forces oppose the driving force of a car?

A

Friction and air resistance.

19
Q

What does the stopping distance if a vehicle depend on?

A

Thinking distance and braking distance

20
Q

What is thinking distance?

A

The distance travelled by the vehicle during the driver’s reaction time.

21
Q

What is braking distance?

A

The distance travelled by the vehicle during the time the braking force acts.

22
Q

What does braking force depend on?

A
  • the speed of a vehicle when the brakes are first applied.

* the mass of the vehicle.

23
Q

What factors can increase the stopping distance of a vehicle?

A
  • tiredness, alcohol and drugs.
  • distractions (mobile phone).
  • high speed.
  • adverse road conditions.
  • poor weather conditions.
  • poorly maintained vehicles.
24
Q

What is mass?

A

The quantity of matter in an object.

25
Q

What is mass measured in?

A

Kilograms (kg)

26
Q

What is weight?

A

The force of gravity on an object.

27
Q

What is weight measured in?

A

Newtons (N)

28
Q

What is the weight of an object with a mass of 1kg?

A

10N

29
Q

What can we say about the motion of a falling object acted on only by gravity?

A

It accelerated at about 10 m/s2.

30
Q

What is the gravitational field strength at Earth’s surface?

A

10N/kg

31
Q

What is the equation of weight?

A

Weight (N) = mass (kg) x gravitational field strength (N/kg)

32
Q

What is drag force?

A

A force opposing the motion of an object due to fluid flowing past the object as it moves.

33
Q

What is terminal velocity?

A

The velocity reached by an object when the drag force on it is equal and opposite to the force making it move.

34
Q

What is the drag force called when the object moves through air?

A

Air resistance.

35
Q

How do we know if an object is elastic?

A

An elastic object regains its original shape when the forces deforming it are removed.

36
Q

How do we measure the extension of an object when it is stretched?

A

The extension is the difference between the length of the spring and its original length.

37
Q

What is Hooke’s law?

A

The extension of a spring is directly proportional to the force applied, provided its limit of proportionality is not exceeded.

38
Q

What is the equation of Hooke’s law?

A

Force applied (N) = spring constant (N/m) x extension (m)

39
Q

What is the spring constant of a spring?

A

The force per unit extension needed to extend the spring, assuming its limit of proportionality is not reached.

40
Q

How does the stiffness of a spring affect the spring constant?

A

The stiffer a spring is, the greater its spring constant is.

41
Q

How can the fuel economy of road vehicles be improved?

A
  • reducing the speed

* fitting a wind deflator

42
Q

What is an average speed camera?

A

Average speed cameras are linked in pairs and they measure the average speed of a vehicle.

43
Q

How do anti-skid surfaces reduce skids?

A

They increase the friction between a car tyre and the road surface.

Physics (5 decks)

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