Topic 1 -forces Flashcards
What is scalar quanitities ?
Scalar quantities have a magnitude (size) only .
-Scalar quanitites do not have a direction .
Give a few examples of scalar quantities .
mass , temperature , spepd ,e enrgy , distace , time .
What is vector wuantities ?
vector quanitities both have magnitude and direction .
GIve a few examples of vector quanitites .
Dispalcement , weight , force , velocity , accleration and momentm
Explain dispalcement
Magnitude -(500m as an example )
and direction example (due West )/
How can we represnent vectors ?
- 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 .
What is the unti for force ?
Newtons .
What two quanitites is force dividied into ?
- Contact Froces
- Non contact forces .
Examples of contact forces .
Objects thae aare physically touching ,
(tension , friction between two objects causing them to slow down , stop )
air resistance .
WHat is normal contct force ?
-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 .
Examples of noncontact forces .
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 .
What is a force ?
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 .
What do Newton’s laws descrie ?
Describe the effect forces have on motion of an object .
What is newtons first law ?
- 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 ).
If forces are balanced …
Resultant force 0 , object will remian stationary .
Velcoity of an objectc will only change if a resultant ofrce si actiong on an object .
If something is moving at a constant sppeeed …
there mus be an eqqual force actiign to on it i opposite direction
Known as resitiive force - friction with air , fricition with road .
What is the resulant force ?
-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
How to draw a free body diagram ?
Draw on for 20N to the right
10N -
- 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 . .
meaning of alitituude
height .
Draw free body diaram for plane flying at constant velocity nd constant alitutude
- 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 .
As aeroplane is moving at a constant velocity …
Forward and backward forces e baalnce .
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 .
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 .
What is gravity ?
A vector quanintit has a magnitude and direction .
What is mass ?
Mass tells us how much matter the object has ini it .
Unit of mas is Kg
scalar quanitity as it has no direcgtioin .
Key idea about mass .
Mass od an obejct does nt depend where object is (elephan oneaarth 5000 kg , on moon also 5000 kg in space also 5000kg)
What is weight ?
- 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 .
What is gravitatoinal field strength of Eafrth ?
- 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 .
Equation of calculaitng weight ?
Weigt (n)=Mass *Gravitiational field strength (N/kg)
W*mg traingleee .
weight of an object …
is direciotnaly propotional to mass of object .
weight fish shape thing to mass .
if we double WEIGHT mass also DOUBLES .
How d we determine an objects weigth ?
calibrated spring balancce - newton metre .
moon gravitiational field strength 1.6 N/kg
What is the ceneter of mass ?
Weight of an object (force due to gravity ) can be considerd to act at a single point - known as centerr of amss .
What happens if you push a box ?
-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 .
How do you calculate work done ?
Work done )J) =Force (N)Distance (m)
Wfd traignle
-distance must be in line with the force .
What happens when a car brakes ?
- 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 . .
Whatd oes it mean distance must be lin line with force .
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 .
What are elastic materials ?
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
Meanng of elastic deformation ?
Object will return to it s original shape .
(strech it ,original shape when force removed
compressed , original shape when force removed .)
In order to change objects length or shape , need more than one force .
Only oen force acting ons statioonary object , forces no longer balanced , so object will just move not change shape .
What are inelastic materials ?
-Do not return to their original shape when forces are removed (polymers )
This inelastic deformtion - it wil remain permanently deformed
What is the calculation to strech an elastic object .
Force (N)= Spring constant (n/m( *Extenstion (m)
-Sme eqution for compression just e stands for compresion .
Joule =N/m
When we strech or compress an object …
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 .
Whaat is hookes law ?
The extension of a spring is directly proportional to the force applied , as long as its limit of proportionality not exceeded .
Equipment for RQP Hooke’s law .
indpeendnet -forces s on spring
dependent - extenstion of spring
-ontrol -set up of equipment ,
Clamp stand two boasses calmmps spring with point metre ruler
- stage for rqq .
Now place a heavy weight on a clamp stand to stop if from fallig over .
- stage for rqq .
- 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 .
- stage of rqp.
3.Bottom of spring has a wooden splint ttached to it as a poitner , Pointer has to be horizontal or inaccurate readings .
4 stage of rqp.
- Now read posotion of poitner on metre rule .
- this is unstreched length of spring (the length with no force attached )
- stage of rqp.
Hang 1N weight on sprign now read positon of poitner on metre rule .
Continue adding as man weight as you need (4 1n weights )
- stage of rqp.
Now work out extension produced by adding each weiight . TO DO THIS SUBRTACT unstreched length from length of each reading .
- stage of rqp.
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 .
Facts about the RQP practical .
- 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 .
Whathappens if we use a rubber band for rqp ?
Check grpah osn sheet .
-NOn liner relationsji .
PROBLEM , what if we add too much weight ?
- 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 .
How do we work out the Spring constant using gtaph ?
-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 .
