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Physics GCSE > Forces > Flashcards

Forces Flashcards

1
Q

What is the difference between a scalar and vector quantity? (give examples)

A

Scalar quantities only have a magnitude (size) e.g speed

Vector quantities have a magnitude AND have a direction e.g velocity

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2
Q

Give the equation for speed:

A

speed = distance/time

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3
Q

Give the equation for acceleration:

A

acceleration = change in velocity/time taken

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4
Q

What is the difference between distance and displacement?

A

Displacement is a vector quantity that gives the distance an object moves in a straight line from a starting point to a finishing point (includes direction). Distance is a scalar quantity and doesn’t include direction.

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5
Q

Give examples of non-contact and contact forces:

A

Non-contact: gravitational force, electrostatic force and magnetic force.
Contact: friction, air resistance, tension and normal contact force.

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6
Q

Give the equation for velocity:

A

velocity= displacement/time

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7
Q

What is mass and inertia?

A
  • Mass is a measure of the amount of matter an object contains.
  • Inertia is how difficult it is to change the object’s motion.
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8
Q

Give the equation for weight: (also what is the value of acceleration due to gravity at the Earth’s surface?)

A

weight = mass*acceleration due to gravity (9.81 m/s^2)

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9
Q

What is a centre of mass?

A

The point through which an object’s weight appears to act. When the centre of mass is moved outside the object’s base, the object will topple.

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10
Q

What is resultant force? (give the equation which is also-)

A

The resultant force is the sum of all of the forces acting on an object. (force = mass*acceleration, Newton’s 2nd Law)

Resultant Force=forces acting in one direction−forces acting in the opposite direction

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11
Q

What is Newton’s 1st Law?

A

The velocity of an object will only change if a resultant force is acting on the object.
If an object is moving and there is no resultant force acting on it, the object will continue moving in the same direction at the same speed.

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12
Q

What is Newton’s 3rd Law?

A

Whenever 2 objects interact, the forces that they exert on (apply to) each other are equal and opposite.

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13
Q

Why must there be two or more forces acting on it to compress, bend or stretch an object?

A

If only one force is acting, the object will just move in the direction of that force.

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14
Q

What is elastic and inelastic deformation?

A

An inelastically deformed object will not return to its original shape when the force stops.
An elastically deformed object will return to its original shape when the force stops.

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15
Q

What might a force acting on an object do to it?

A

A force acting on an object may change its size or

shape.

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16
Q

What is the equation for Hooke’s Law? (what is spring constant)

A

force = spring constant*spring extension (spring constant is thought of as the stiffness of a string)

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17
Q

What does Hooke’s Law and the Limit of Proportionality tell us?

A
  • Extension is directly proportional to the force applied: F=ke
  • If a spring is over-stretched, it will not return to its original length
  • The higher the spring constant, the stiffer the spring.
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18
Q

What happens when we compress a spring?

A

Elastic potential energy is stored in the spring.

The elastic potential energy stored in a spring is equal to the work done when stretching it.

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19
Q

How can we read the elastic potential energy from a force-extension graph?

A

The area under the graph.

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20
Q

Give the equation for elastic potential energy:

A

Ee= 1/2ke^2

21
Q

When work is done on a spring, what is stored in the spring?

A

Elastic potential energy

22
Q

When an object is in free fall, what forces act on it? At what rate does it accelerate?

A
  • Only its own weight will act on it due to gravity.

- At a constant rate.

23
Q

Why do objects falling in the Earth’s atmosphere not accelerate indefinitely? (which of newton’s law does this relate to?)

A

Air resistance (frictional force) slows down a falling object.
The force due to air resistance increases as the speed of a falling object increases.
(3rd)

24
Q

What is momentum and what is its equation?

A

The momentum of an object is its tendency to keep moving in the same direction.
(p = mv and units are kgm/s)

25
Q

What does the law of conservation of momentum state?

How do you calculate change in momentum?

A

Momentum can not be created or destroyed.
Change in momentum = mv - mu, where m is mass, u is the initial velocity of an object and v is the final velocity of an object. (Δp = F x t)

26
Q

How do safety features in a car reduce the force felt by a person in a crash?

A

Cars have safety features that absorb the kinetic energy transferred by collisions.
Injuries are reduced by absorbing energy when these features change shape.
The time taken for the change in momentum to happen increases so the forces are reduced.

27
Q

What is a moment? (what is the equation)

A

The turning effect of a force around a pivot. (moment = force × distance)

28
Q

How can you magnify the force in a moment?

A

By exerting force further away from the pivot.

29
Q

What is true of an object in equilibrium?

A

An object in equilibrium will not turn or accelerate - there is no overall (resultant) force and the clockwise moments are equal to the anticlockwise moments.

30
Q

What is true of circular motion?

A

An object moving in a circular motion is constantly changing direction.
A change in direction gives a change in velocity because velocity is a vector quantity.
Acceleration equals the change in velocity per unit time, so an object travelling in a circular motion at a constant speed is accelerating.
The resultant force always acts towards the centre of the circle and the object is always accelerating.

31
Q

What is pressure? (equation?)

A

When particles collide with the walls of their container. the particle exerts a force on the container at right angles and the container exerts a force on the particle.
(pressure = force/area)

32
Q

What is atmospheric pressure?

A

Atmospheric pressure is the force per unit area created by the weight of the air (particles) in the atmosphere. We feel the weight of the atmosphere as 100 kilo Pascals.

33
Q

Why is air pressure lower the higher you are?

A

There is less air above you, so the weight of the air is lower, meaning the force is decreased.

34
Q

What is the equation for liquid pressure?

A

Liquid pressure = density x gravitational field strength x depth

35
Q

What is it that created liquid pressure?

A

The weight of the liquid above

36
Q

Describe upthrust:

A

-Upthrust = weight of liquid displaced
The upthrust that acts on an object is equal to the weight of the liquid that has been forced away (displaced) by that object.

37
Q

How do submarines control their depth in water?

A

-When a submarine wants to come up to the surface, it fills its tanks with compressed air to reduce its weight.
Weight becomes less than upthrust so the submarine rises.
-When a submarine wants to sink, it fills its tanks with water to increase its weight.
This means the submarine’s weight is greater than the upthrust and it sinks.

38
Q

How do you calculate liquid pressure difference?

A

Δp=ρgΔh
(The pressure difference is equal to the density of fluid multiplied by the gravitational field strength multiplied by the change in depth)

39
Q

What is stopping distance and how is it calculated?

A

Stopping distance is the distance it takes a car to stop in an emergency.
Stopping distance = thinking distance + braking distance.

40
Q

What is thinking distance?

A

The time it takes for a driver to react to a situation is their reaction time.
The thinking distance is the distance travelled between when the driver realises they need to brake and when they apply the brakes.

41
Q

What is braking distance?

A

The distance the car travels between the driver applying the brakes and the car coming to a stop.

42
Q

What factors influence thinking distance?

A
  • drugs or alcohol (slows reaction time)
  • distractions (slows reaction time)
  • tiredness (slows reaction time)
43
Q

What factors influence braking distance?

A
  • condition of a car (braking distance will increase)
  • initial car speed
  • road conditions
44
Q

Describe braking:

A
  • Pushing the brake pedal means brake pads are pressed onto the wheels.
  • This contact causes friction, causing work to be done.
  • Work done converts energy from kinetic energy in the wheels to thermal energy in the brakes.
  • The temperature of the brakes then increases.
45
Q

What affects work done when braking?

A
  • higher speed (increases)
  • greater mass (increases)
  • better grip (decreases)
46
Q

Equation for work done braking:

A

F d = ½mv^2

47
Q

How can braking force affect deceleration?

A

The greater the braking force, the greater the deceleration of the vehicle.

48
Q

Why can large decelerations be dangerous to the vehicle?

A

Large decelerations can cause brakes to overheat and/or the car to skid. It transfers more stopping force to passengers which is harmful.

Physics GCSE (1 decks)

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