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A Level Physics > 3 Forces and Motion > Flashcards

3 Forces and Motion Flashcards

1
Q

Instantaneous speed

A

The speed of the car over a very short interval of time

Found by drawing tangent to distance-time graph at that time

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2
Q

Average velocity graph

A

Change in displacement/ time taken

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3
Q

Average acceleration equation

A

Change in velocity/ change in time

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4
Q

Acceleration from graph

A

Gradient of velocity-time graph

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5
Q

Stopping distance

A

Thinking distance + braking distance

Total distance travelled from when the driver first sees a reason to stop, to when the vehicle stops

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6
Q

Thinking distance

A

Distance travelled between the moment when you first see a reason to stop, to the moment when you use the brake

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7
Q

Braking distance

A

The distance travelled from the time the brake is applied until the vehicle stops

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8
Q

Thinking distance equation

A

Speed x reaction time

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9
Q

Free fall

A

When an object is accelerating under gravity, with no other force acting on it

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10
Q

Determining g in lab experiments

A

Electromagnet and trapdoor
Light gates
Taking photos of dropped ball next to metre rule

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11
Q

The moment of a force

A

The turning effect of a force about some axis or point

Moment= force x perpendicular distance of the line of action of force from the axis or point of rotation

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12
Q

Perpendicular distance

A

Use the perpendicular distance in calculations involving moments, not just the distance from force to pivot

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13
Q

The principle of moments

A

For a body in rotational equilibrium, the sum of the anti-clockwise moments about any point is equal to the sum of the clockwise moments about the same point

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14
Q

Torque of a couple

A

The moment of a couple is known as a torque. The torque of a couple is defined as
torque of the couple = one of the forces X perpendicular separation between the forces
=Fd

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15
Q

Density

A

Mass per unit volume

Kgm-3

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16
Q

Pressure

A

Normal force exerted per unit cross sectional area

Nm-2 or Pa

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17
Q

Pressure in liquids

A

p=hpg
Height x density x acceleration of free fall
Pressure at base is equal to the weight of column divided by cross sectional area

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18
Q

Archimedes’ principle

A

The upthrust exerted on a body immersed in a fluid is equal to the weight of the fluid that the body displaces

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19
Q

When will an object sink

A

If the upthrust is less than the weight of the object

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20
Q

Floating objects

A

The upthrust equals the eight of the objects

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21
Q

Work done

A

Energy transferred

Nm or J

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22
Q

Work done at angle to motion

A

Work done W= (F cos(theta)) * x

W=Fxcos()

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23
Q

Energy

A

The capacity for doing work
Scalar
Joules

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24
Q

Forms of energy

A 
Kinetic energy
Gravitational potential 
Chemical
Elastic potential 
Electrical potential 
Nuclear
Radiant/electromagnetic 
Sound
Thermal
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25
The principle of conservation of energy
The total energy of a closed system remains constant: energy can never be created or destroyed, but it can be transferred from one form to another
26
Kinetic energy
Energy associated with an object as a result of its motion | Kinetic energy = 0.5 X mass X velocity2
27
Gravitational potential energy
The capacity for doing work as a result of an object’s position in a gravitational field Gravitational potential energy = mass X gravitational field strength X height
28
Power
The rate of work done | Js-1 or W
29
Tensile forces
Forces that produce extension
30
Compressive forces
Forces that shorten an object
31
Hooke’s law
The extension of the spring is directly proportional to the force applied. This is true as long as the elastic limit of the spring is not exceeded
32
Elastic deformation
Means that the spring will return to its original lights when the force is removed
33
Plastic deformation
Permanent structural changes to the spring occur and it does not return to its original length when the force is removed
34
Force constant K
For a spring obeying hooke’s law, the applied force F is directly proportional to the extension x.Therefore F =kx
35
What shows work done on a force – extension graph
Area under the graph
36
Loading and unloading metal wire
Follows Hooke’s law until the elastic limit of the wire Beyond the elastic limit it is parallel to the loading graph but not identical to it The wire is permanently extended after the force is removed- it’s longer than it was at the start
37
Loading and unloading rubber
Don’t obey Hooke’s law Rubber band will return to its original length after the force is removed- elastic deformation The loading and unloading graphs are both curved and are different Hysteresis loop
38
Unloading and loading polythene
Doesn’t obey Hooke’s law | Suffer plastic deformation under little force
39
Tensile stress
The force applied per unit cross sectional area of the wire | Sigma is symbol for tensile stress
40
Tensile strain
``` The fractional change in the original length of the wire Curvy E (epsilon) is tensile strain ```
41
Ultimate tensile strength
The maximum stress that a material can withstand when being stretch before it breaks Beyond this point the material may become longer thinner at its weakest point, a process called necking
42
Breaking point
Where the material eventually snaps from the stress it’s put under
43
Breaking strength
The stress value at the point of fracture
44
Strong material
One with a high ultimate tensile strength
45
Young modulus
Tensile stress/ tensile strain The ratio of stress to strain for a particular material Gradient of stress-strain graph Nm-2 or Pa
46
Stress-strain graph for brittle materials
Straight line. 2 arrows pointing into each other | Ultimate tensile strength is same as breaking strength
47
Polymeric materials
Materials that consist of long molecular chains | Polythene and rubber
48
Stress-strain graph for rubber
Marble swirl shape????? | Clockwise arrows
49
Stress-strain graph for polythene
Straight line then levels off
50
Newton’s first law of motion
An object will remain at rest or continue to move with constant velocity unless acted upon by a resultant force
51
Newton’s third law of motion
When two objects interact, they exert equal and opposite forces on each other
52
Types of interaction
All interactions can be explained in terms of four fundamental forces- gravitational, electromagnetic, strong nuclear and weak nuclear. The two nuclear forces have a very short range and so very little impact on things we observe in daily life. When you push your hands together, the contact force you feel is due to the electrostatic repulsive forces between the electron clouds around the atomic nuclei in your hands
53
Momentum
Momentum= mass x velocity | Kg m s-1
54
Conservation of momentum principle
For a system of interacting objects, the total momentum in a specified direction remains constant, as long as no external forces act on the system
55
Total momentum before collision=
Total momentum after collision
56
Zero momentum example- gun
A gun recoils when a bullet is fired. The total momentum of this system remains the same and is equal to zero. The momentum of the gun and the momentum of the bullet have the same magnitude but act in opposite directions
57
Two types of collisions
Perfectly elastic | Inelastic
58
Summary of perfectly elastic collision
Momentum- conserved Total energy- conserved Total kinetic energy- conserved
59
Summary of inelastic collision
Momentum- conserved Total energy- conserved Total kinetic energy- not conserved
60
Newton’s second law of motion
``` The net (resultant) force acting on an object is directly proportional to the rate of change of its momentum, and is in the same direction Net Force= change in momentum/time Also F=ma ```
61
Why is momentum conserved in collisions?
The net force on the objects in a closed system is zero. According to Newton’s second law change in momentum/time=0. The change in momentum of both objects must be zero; therefore, the total momentum of the objects doesn’t change Momentum is always conserved
62
Impulse of a Force
Forces accelerating or decelerating an object usually change over time e.g. kicking a ball. This type of motion can be analysed using the idea of impulse Impulse of a Force= change in momentum =Ft
63
Unit of impulse
Ns | Kg m s-1
64
Area under force-time graphs
Impulse | Area=Ft

A Level Physics (15 decks)

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