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Y11 PHYSICS > FORCES AND MOTION > Flashcards

FORCES AND MOTION Flashcards

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1
Q

What can forces change/transfer?

A
  • Forces can change the SPEED of objects – either getting it to start moving, making it stop or making it go faster or slower.
  • Forces can change the DIRECTION of objects - stop it moving in a straight line, or getting it to deflect/bend away from the direction it was going.
  • Forces can change the SHAPE or SIZE of objects – stretching, bending, twisting or squashing.
  • Forces transfer energy.
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2
Q

Contact forces?

A

-MECHANICAL – pushes or pulls, causing objects to move or change speed, often called THRUST.
-DRAG – a force that slows objects down – which can be called FRICTION, AIR RESISTANCE or WATER RESISTANCE.
-UPTHRUST – the force that pushes up from water.
-NORMAL or REACTION – the perpendicular force
that pushes up from the ground or solid surface.
-TENSION – the ELASTIC force in a rope or cable

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3
Q

Non-contact forces?

A
  • WEIGHT or GRAVITATIONAL – the force due to gravity causing objects to be pulled downwards
  • ELECTROSTATIC – the force between two electrically charged objects (which can be a force of attraction between unlike charges or repulsion for like charges)
  • MAGNETIC – the force between two magnetic objects (which can be a force of attraction between unlike poles or repulsion for like poles)
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4
Q

Friction?

A

• Friction is a force that opposes motion.
• Friction from fluids (such as liquids or gases, like air) is
normally called resistance or ‘drag’.
• Air resistance and water resistance are examples of these.
• By making the shape of moving objects streamlined, the size of these forces can be reduced.
• Friction (all types) always INCREASES as speed INCREASES

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5
Q

What is a scalar and an example of it?

A

-A scalar quantity only has MAGNITUDE (or size)

  • volume
  • density
  • speed
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6
Q

What is a vector and examples?

A
  • A vector quantity has MAGNITUDE and DIRECTION
  • A VECTOR can be represented by an ARROW

-FORCE is a VECTOR QUALITY – it has a size (magnitude) and direction

  • force
  • position
  • velocity
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7
Q

Speed equation?

A

Speed = distance/time

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8
Q

Velocity equation?

A

Velocity= displacement/time

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9
Q

Acceleration equation ?

A

-Acceleration=change in velocity/time

  • a= acceleration (m/s2)
  • u= initial velocity (m/s)
  • v = final velocity (m/s)
  • t = time (s)
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10
Q

What does a steeper straight gradient show on a velocity time graph?

A

A faster constant acceleration

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11
Q

What does a flat gradient show on a velocity time graph?

A

Constantly velocity (zero acceleration)

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12
Q

What does a negative gradient show on a velocity time graph?

A

Negative acceleration or deceleration

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13
Q

Resultant force?

A
  • The overall effect of a lot of forces acting together – is called the RESULTANT FORCE
  • It is the one single force that would affect the object the same way as all the other forces combined
  • Forces in the SAME direction ADD UP
  • Forces in the OPPOSITE direction SUBTRACT from each other
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14
Q

What is Newtons 1st law?

A

• An object will remain at rest, or continue to move at constant velocity, unless it is acted upon by an external force.

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15
Q

Newtons 1st law explanation?

A

• If the resultant force acting on an object is zero and:

  • the object is at rest - the object remains at rest.
  • the object is moving - the object continues to move at the at the same velocity (the same speed and the same direction)

• If the resultant force is non-zero, you get a change in velocity (it changes speed and/or direction) – whether it was at rest before that or was already moving

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16
Q

Balanced forces?

A

-When the resultant force is zero – the forces acting on the
object are ‘balanced’ or in ‘equilibrium’
-No change in velocity (speed in a certain direction) takes place e.g,

A stationary object stays stationary
A moving object stays moving at the same velocity

17
Q

Unbalanced forces?

A

-When the resultant force is non-zero – the forces acting on the object are ‘unbalanced’

  • A change in velocity takes place (acceleration)
    e. g, A stationary object begins to move (accelerate)

-A moving object starts to accelerate in the direction of the resultant force

18
Q

Newtons 2nd law?

A
  • When a force acts on an object, the object accelerates in the direction of the force.
  • The size of the acceleration depends on the size of the force and the mass of the object
19
Q

Force equation?

A

-Force = mass x acceleration

  • F = force (N)
  • m = mass (kg)
  • a = acceleration (m/s2)
20
Q

Weight equation?

A

-weight=mass x gravitational field strength

  • w=weight (N)
  • m=mass (kg)
  • g=gravitational field strength (N/kg)
21
Q

Terminal velocity?

A
  • Any object moving through a fluid (such as air) experiences a resistive force opposite to its motion. This is called air resistance.
  • The greater the speed of motion – the greater the air resistance force.
  • When air resistance is equal and opposite to the force causing the motion – the object has balanced forces (no resultant force) and it is now at a constant velocity – called the TERMINAL VELOCITY
  • A skydiver reaches this when their weight (W = mg) moving them down, is balanced by the air resistance (FAIR) acting up!
22
Q

Sky diver?

A
  • At first a skydiver increases in velocity as his weight is greater than the air resistance opposing his motion
  • As he speeds up, the air resistance increases
  • When he reaches terminal velocity his weight (downwards force) is balanced by the air resistance (upwards force) – he is now at a constant velocity!
23
Q

Parachutes?

A

• The large surface area of a parachute provides lots of air resistance!
• When opened, the upwards force will be much greater than the downwards force (weight) – so the skydiver slows down
• As they slow down, air resistance FAI
reduces – until we have balanced forces again – but at a much lower terminal velocity - about 30 km/h (around 18 mph)
• They stop on the ground, as weight down = normal/reaction force up!

24
Q

Stopping distance equation?

A

Stopping distance=thinking distance + braking distance

25
Q

Stopping distance?

A
  • The stopping distance is how far a vehicle travels before it stops. It is made up of two parts:
  • Thinking distance – distance a vehicle travels while the nerve cell message travels from your eyes to your brain and back to your foot on the brake pedal
  • Braking distance – distance a vehicle travels while it is slowing down after pressing the brake pedal
26
Q

Thinking distance equation?

A

Thinking distance=speed x reaction time

27
Q

Thinking distance?

A
  • Thinking distance depends on the car’s speed and driver’s reaction time
  • A driver’s reaction time will be slower than usual if they are tired, taken alcohol or drugs, or are distracted in other ways, such as mobile phones, music players etc.
28
Q

Braking distance?

A

• Braking distance depends on the car’s speed - doubling the speed of a car increases braking distance by four times!
It also depends on:
• Mass/weight – more kinetic energy! • Condition of tyres
• Condition of brakes
• Road conditions – water, ice, snow…

29
Q

Elasticity?

A
  • An object that returns to its original shape when the force stops acting on it is an elastic object.
  • Whenever an elastic object is stretched or compressed, energy is transferred to change its shape, size or length.
  • It is stored as elastic potential energy.
30
Q

Hooke’s law?

A
  • When a spring (or rubber band) experiences a stretching force, it will increase in length (extension beyond its original length) as the force increases.
  • Robert Hooke found that for an elastic object (like a spring), the force applied is directly proportional to the extension.
  • This force-extension relationship is called HOOKE’S LAW. The gradient of the straight line is called the spring constant (how stiff the spring is)

Y11 PHYSICS (5 decks)

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