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Physics > Topic 1 -forces > Flashcards

Topic 1 -forces Flashcards

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1
Q

What is scalar quanitities ?

A

Scalar quantities have a magnitude (size) only .

-Scalar quanitites do not have a direction .

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2
Q

Give a few examples of scalar quantities .

A

mass , temperature , spepd ,e enrgy , distace , time .

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3
Q

What is vector wuantities ?

A

vector quanitities both have magnitude and direction .

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4
Q

GIve a few examples of vector quanitites .

A

Dispalcement , weight , force , velocity , accleration and momentm

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5
Q

Explain dispalcement

A

Magnitude -(500m as an example )

and direction example (due West )/

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6
Q

How can we represnent vectors ?

A
  • Vectors can be reperesetned using an arrow
  • Length of the arrow is equal to the magntidue of the vector ,
  • Direction of the arrow is direction of the vector .
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7
Q

What is the unti for force ?

A

Newtons .

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8
Q

What two quanitites is force dividied into ?

A
  • Contact Froces

- Non contact forces .

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9
Q

Examples of contact forces .

A

Objects thae aare physically touching ,
(tension , friction between two objects causing them to slow down , stop )
air resistance .

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10
Q

WHat is normal contct force ?

A

-Lamp exerts force on tbale , table exeerts force on lamp , only happens if objects are in direct contact .
an object exetrs a force on the surface the surface exerts a force on the object .

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11
Q

Examples of noncontact forces .

A

Objects that are physicaly separated .
Gravaitional forces - atratcts alll objects to other forces .
Electrosatic force - between two chatged objects , same charges repulsion , opposite atraction .
Magnetic force - experinced by objects in a magnetic ofrce .

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12
Q

What is a force ?

A

A force is a push or pull that acts on an object due to its interaction with another object .
-forces are vector qunaities as they have both magnitude and direction .

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13
Q

What do Newton’s laws descrie ?

A

Describe the effect forces have on motion of an object .

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14
Q

What is newtons first law ?

A
  • If the resultant force action on a stationary object is zero , objec will remian stationary .
  • If resualtant force action on an moving object si zero , it will continue moving in same direction at smae speed (velocity ).
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15
Q

If forces are balanced …

A

Resultant force 0 , object will remian stationary .

Velcoity of an objectc will only change if a resultant ofrce si actiong on an object .

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16
Q

If something is moving at a constant sppeeed …

A

there mus be an eqqual force actiign to on it i opposite direction
Known as resitiive force - friction with air , fricition with road .

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17
Q

What is the resulant force ?

A

-The resulant force is a single force that has the same effect as all the original forces acting otgether , Working out resultant force , we subtract smaller froce from larger force .
to 20right ten to left
-20-10 = 10N to the right

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18
Q

How to draw a free body diagram ?
Draw on for 20N to the right
10N -

A
  • Objects are drawn as a point .
  • Force are drawn as arrows at the starting point .
  • Length of arrow sgiws size of force ,
  • direction of arrow direction of force . .
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19
Q

meaning of alitituude

A

height .

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20
Q

Draw free body diaram for plane flying at constant velocity nd constant alitutude

A
  • contant alitidue so downwards force weight but also opposite euqal force lift .
  • thurst forward porvided by engine . consant velocity , so air resistance acting in opposite direction .
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21
Q

As aeroplane is moving at a constant velocity …

A

Forward and backward forces e baalnce .

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22
Q

What if two forces accting at angle ..
Froces acting on object , one magnitude 10n other at 8n with angle 30 degrees beween two forces , calculae resultant forces .

A

1.dot as object , have a key (like 5 cm is 1n )
- draw 10 n line
use portractor mesaure 30 degrees anfle , then draw 8n line .
-create parallelogram - make 8n line from oroginal 10n line first .
-then 10 n line from 8cm line
-draw line from one side of parallelogram to other side and then thats resultant force .

23
Q

What is gravity ?

A

A vector quanintit has a magnitude and direction .

24
Q

What is mass ?

A

Mass tells us how much matter the object has ini it .
Unit of mas is Kg
scalar quanitity as it has no direcgtioin .

25
Q

Key idea about mass .

A

Mass od an obejct does nt depend where object is (elephan oneaarth 5000 kg , on moon also 5000 kg in space also 5000kg)

26
Q

What is weight ?

A
  • Weight og an object is force acting on it due to gravity .
  • Unit of weight is newton .
  • weight of ano onnject odes dpened where it is .
27
Q

What is gravitatoinal field strength of Eafrth ?

A
  1. 8N/kg aka gravitiational field strength - this measures he force of gravity in a particular location .
    - object on surface of earth , esperiences gravitational force to cenrer of earth .
28
Q

Equation of calculaitng weight ?

A

Weigt (n)=Mass *Gravitiational field strength (N/kg)

W*mg traingleee .

29
Q

weight of an object …

A

is direciotnaly propotional to mass of object .
weight fish shape thing to mass .
if we double WEIGHT mass also DOUBLES .

30
Q

How d we determine an objects weigth ?

A

calibrated spring balancce - newton metre .

moon gravitiational field strength 1.6 N/kg

31
Q

What is the ceneter of mass ?

A

Weight of an object (force due to gravity ) can be considerd to act at a single point - known as centerr of amss .

32
Q

What happens if you push a box ?

A

-Friction of box causes the temperature to increase .
-Chemica energy store in persons muscle is converted to thermal energy store of box .
Whenever a force is used to move an object ,, energy is ransferred known as WORK .

33
Q

How do you calculate work done ?

A

Work done )J) =Force (N)Distance (m)
Wfd traignle
-distance must be in line with the force .

34
Q

What happens when a car brakes ?

A
  • Moving an object has a kinetic energys tore - durign braking , brake presses against whell .
  • Force of fricition now acts beteween brake and the wheel.
  • Kinetic energy store of car is now moved into thermal energy store of the brakes
  • Temperature of brakes iscrease athte same ime , car slows down , and it loosees kinetic energy . .
35
Q

Whatd oes it mean distance must be lin line with force .

A

If a person is walking - weight acts verticlay downwards on vertical ditance , itd the only relevant force , chemical energys tore of human goes to gravititon potential energy .

36
Q

What are elastic materials ?

A

Materials that will allways return to their original length , or shape if we take away the forces acting on them (rubber band , earser , spring ).Elastic deformation

37
Q

Meanng of elastic deformation ?

A

Object will return to it s original shape .
(strech it ,original shape when force removed
compressed , original shape when force removed .)

38
Q

In order to change objects length or shape , need more than one force .

A

Only oen force acting ons statioonary object , forces no longer balanced , so object will just move not change shape .

39
Q

What are inelastic materials ?

A

-Do not return to their original shape when forces are removed (polymers )
This inelastic deformtion - it wil remain permanently deformed

40
Q

What is the calculation to strech an elastic object .

A

Force (N)= Spring constant (n/m( *Extenstion (m)
-Sme eqution for compression just e stands for compresion .
Joule =N/m

41
Q

When we strech or compress an object …

A

we are using a force to do work , Elastic pontential energy stored in an object ,
work done = elastic potential nergy
only true if object NOT INELASTICALLY DEFORMED .

42
Q

Whaat is hookes law ?

A

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

43
Q

Equipment for RQP Hooke’s law .
indpeendnet -forces s on spring
dependent - extenstion of spring
-ontrol -set up of equipment ,

A 
Clamp stand
two boasses                               
calmmps
spring with point
metre ruler
44
Q
  1. stage for rqq .
A

Now place a heavy weight on a clamp stand to stop if from fallig over .

45
Q
  1. stage for rqq .
A
  1. next we attach a metre rule and spring .

- Top of spring must be at zero on the metre rule , metre rule ahs to be vertical for accurate readings .

46
Q
  1. stage of rqp.
A

3.Bottom of spring has a wooden splint ttached to it as a poitner , Pointer has to be horizontal or inaccurate readings .

47
Q

4 stage of rqp.

A
  1. Now read posotion of poitner on metre rule .

- this is unstreched length of spring (the length with no force attached )

48
Q
  1. stage of rqp.
A

Hang 1N weight on sprign now read positon of poitner on metre rule .
Continue adding as man weight as you need (4 1n weights )

49
Q
  1. stage of rqp.
A

Now work out extension produced by adding each weiight . TO DO THIS SUBRTACT unstreched length from length of each reading .

50
Q
  1. stage of rqp.
A

Plot grpahif extdension (y) against weight (x) .

  • I rqp meant tow ork out weight of mystery object .
  • to do this measure extenstion of spring when stone is hanging from it , read from graph to measure wiegt of stone .
51
Q

Facts about the RQP practical .

A
  • Graph is a striaght line goign through the prpigin (zero) .
  • this itells us extension directly propotioanl to the weight .
  • Linear (striaght) elationship between force and extension hence striaght line . .
  • Can see spring is elastic as if we were to remove weight , extension returns to xero .
52
Q

Whathappens if we use a rubber band for rqp ?

A

Check grpah osn sheet .

-NOn liner relationsji .

53
Q

PROBLEM , what if we add too much weight ?

A
  • Chec what graph looks like striaght and then goes up .
  • shows non-linear as w hae overstreched spring
  • the spring would still show an extention even if we tooka ll weight off INELASTIC DEFORMATION ,w e haev exceeded springs limit of proptionality .
54
Q

How do we work out the Spring constant using gtaph ?

A

-Use striaght bit limit of propotioanlity bit NOT EXCEEDED BIT .

Divide force (weight / byt extenstion . Can do for any prt of graph apart from exeeded limit of proportionality .

Physics (20 decks)

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