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GCSE Physics > Forces > Flashcards

Forces Flashcards

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1
Q

What is a vector

A

Has both magnitude and direction

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2
Q

What is a scalar

A

Only has magnitude and no direction

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3
Q

Examples of vectors and scalar quantities

A

Vedtor= force,velocity,displacement,acceleration,momentum, etc

Scalar= speed,distance,mass,temperature,time,etc

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4
Q

What is contact force

A

When two objects are touching for a force to act

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5
Q

What is non-contact force

A

Forces that don’t need to touch for a force to act

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6
Q

What is newtons third law

A

When two forces interact the ths force acting on each other are equal and opposite

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7
Q

Examples of contact and non-contact forces:

A

Contact force: Friction,air resistance,tension in ropes, normal contact force, etc

Normal contact force: magnetic force,gravitational force,electrostatic force

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8
Q

Calculation for weight

A

Weight = mass X gravitation field strength

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9
Q

How should free doagrams be drawn provide an example

A

Skydiver falling down.

Arrow labelled weight pointing down below him which isn longer then the arrow labelled air resistance pointed up above the skydiver.

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10
Q

How can resultant force be calcualted

A

Adding the forces going in the same direction and subtracting them from the opposite e,g:

<—–1200N[……………]——>1000N

1200N-1000N=200N to the left

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11
Q

Calculate work done

A

W= F X s

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12
Q

How to use scale drawing for resultant force

A

1) draw all the force on an object to scale

2)Draw a straight line from the start of the first force to the end of the last force - this is the resultant force

3) Measure the length of the resultant force on the diagram to find the magnitude and angle to find the direction of the force

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13
Q

Is the resultant force is zero what are the force in the object in

A

Equillibrium

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14
Q

How to resolve a force

A

Split it into two components by drawing a scale grid. Draw the force to scalw then add a horizontal and vertical components on the grid line and measure

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15
Q

What is elastically deformed and inelastically deformed mean

A

Elastically deformed: It can go back to its orginal shape and length after the force has been removed

Inelastically deformed: it doesn’t return to its orginals haoe and length after the force has been removed

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16
Q

How to calculate force

A

Force= spring constant X extension

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17
Q

Why is there a limit to the amount of force applied to an object for the extension to increase

A

There is a maximum force above which the graph curves, extension no longer proportional to force. Limit of proportionality.

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18
Q

Required practical: investigate the link between force and extension

A

Make sure you have a weight stand with a clamp attached to the top hanging a spring with a hanging mass clipped onto the spring with extra identical masses and a ruler to measure the spring extension

1) Measure the natural length of the springs with nonload with a ruler clamped to the stand. Take the reading at eye level with a marker the add a thin strip of tape at the bottom of the spring to make readings more accurate.

2) Add mass to the spring and allow it to come to rest. Record the mass and measure the new length of the speing. The extension is change in length

3) Repeat process until you have enough measurements

4) Plot a force-extension graph of results

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19
Q

How to calcuakte elastic potential energy

A

Ee=1/2Ke^2

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20
Q

What is distance

A

It is how far an object has moved- scalar

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21
Q

What is displacement

A

Displacement vector- measures the distance and direction from the starting to point to the end

22
Q

What is speed

A

Speed is how fat you are going with no rgeard direction

23
Q

What is velocity

A

Its speed in a given direction

24
Q

Calculation for speed

A

S= Vt

25
Q

Typical speeds for eveyday objects

A

Person walking-1.5m/s

Person running-3m/s

Person cycling-6m/s

Car mocvin 25m/s

Train moving 30m/s

Plane moving-250m/s

26
Q

What is acceleration

A

Change in velocity in a certain amount of time

27
Q

How to calcuate acceleration

A

∆. v
A=———
T

28
Q

Calculation for uniform acceleration

A

V^2 - u^2 =2as

29
Q

What do different lines in distance time graph represent

A

Gradient=speed - distance/time

Flat section- stationary

Straight uphill constant acceleration

Straight downhill constant deceleration

30
Q

What do different lines in a velocity time graph represent

A

Gradient= acceleration- velocity/time

Flat section- steady speed

Steeper the graph the greater the acceleration/deceleration

Curve is change in aceleration/deceleration

31
Q

What will always stop an object in motion

A

Friction acts in the opposite direction to movement . If the driving force is balanced with the frictional force the vehicle will travel at a steady speed. Friction can be reduced by using lubricants

Air resistance and drag will reduce the speed of a vehicle. If an object is more streamlined it will reduce the drag

32
Q

What happens to an object when it reaches terminal velocity

A

When an object falls the force of gravity is greater then the frictional force slowing it down, it accelerates.

As speed increases the friction builds up.

Acceleration reduced until frictional force is equal to the accelerating force (resultant force 0)

It will reach its max speed or terminal velocity and will fall at a steady speed

33
Q

What does terminal velocity depend on provide an example

A

How streamlined the object is

The surface area of the object-larger it is the lower the terminal velocity

Marble will fall at a greater terminal velocity then a beach ball since more drag is acting on the beach ball. The the beach ball spends less time accelerating before the drag is large enough to equal the accerlerating force

34
Q

What is newtons first law

A

If the resultant force on a stationary object is 0, the object will remain stationary. If the resultant force of s moving object is 0 it will carry on moving at the same velocity.

35
Q

Calculation for resultant force

A

Resultant force= mass X acceleration

36
Q

What is newtons second law

A

The acceleration of an object is proportional to the resultant force acting on the object and is inversely proportional to the mass of an object

p=mv

37
Q

What is inertia

A

If an object is at rest it stays at rest and if its in motion it stays in motion

Inertia mas= measures how difficult it is to change the velocity of an object

Inertial mass- F=ma

38
Q

What is newtons third law

A

When two objects interact,the forces they exert on each orher are equal and opposite

39
Q

Required practical:investigate how mass and force affect acceleration

A

Setup: trolley with card ontop-behind starting line attached to a string around a pulley holding a hook with masses- through a light gate connected to a data logger

1) set up the trolley so it holds 2 piece of card with a gap inbetween that will interupt the light gate

2) Input the length of light card that will pass through the light gate. It can calculate the acceleration

3) Connect the trolley to a piece of string that goes over a pulley and is connected on the other side to a hook (that you know the masses of using a balance)

4)The weight of the hook and any masses attached to it will provide accelerating force, equal to the mass of the hook X acceleration due to gravity.

5) Make a starting point on the table using a trolley and then release it

6) record the acceleration measured by the light gateas the trolley passes it

7) Repeat this with different masses

To investigate effect of mass place all the masss allo ont he hook and tranfer to the trolley one at a time

To investigate effetd of force place the masses all on the trolley and transfer to the hook one at a time

40
Q

Calculation stopping distance

A

Stopping distance= thinking distance + braking distance

41
Q

What is thinking distance

A

How far the car travels during the drivers reaction tims

42
Q

What is braking distance

A

The distance taken to stop under the braking force

43
Q

What is thinking distance affected by

A

Speed- faster your going the further you travel

Recation time- the longer your reaction time the longer your thinking distance

44
Q

What is braking distance affected by

A

Your speed- faster a vehicle travels the longer it stops

Weather/friction- wet or icy or oily/ less grip causes tyres to skid

Condition of tyres- baldntyres cannot get rid of water (skidding)

Quality of brakes- brakes worn or faulty applies less force

45
Q

How to estimate the forces involved in acceleration of vehciles:

A car travelling at a typical speed stops 25m ahead. Estimate the braking force of needed to produce the deceleration

A

1) assume the deceleration is uniform and rearrange v^2-u^2=2as to find deceleration
V=-25m/s M=-1000kg

2) Use F=mas, M=-1000kg. A=(v^2 - u^2) /2s = (0^2-25^2) / (2 X 25) =-12.5
F=1000 X 12.5 =12500 N , F=-125000N

46
Q

What can reaction time be affected by

A

Tiredness , drugs,alcohol and distractions

47
Q

Typical speed for feaction time

A

0.2-0.9 s

48
Q

Expeirment to find reaction time of a person

A

1) sit with you arm resting over the edge of a table and get someone to place a ruler lined up inbetwen your thumb and forefnger at zero (third person may be needed to check at eye level)

2) The ruler holder should drop the ruler without warning and the person catching should catch it by closing their thumb and fingers as quick as posisble.

3) The measurement on the ruler at the point of where it is caught is how far the ruler dropped
________________
4) for e.g if it was 20cm U=0, A=9.8m/s^2 and S=0.2m V=/2 X 9.8 X 0.2 + 0 =1.97m/s

T= change in V / A=1.97 /9.8 =0.202= reaction time

5) Repeat many times and calculate a mean. You may also compare with distractions or stimulant

49
Q

How to calculate momentum

A

Momemtum= mass X velocity

50
Q

What is the conservation of momentum

A

In a closed system, the total momentum before an event is equal to the total momentum after the event.

GCSE Physics (8 decks)

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