Chapter 7 Flashcards
Newton first law
An object will continue to be at rest or move at uniform velocity unless a resultant force is after omnitn
Newton’s third law
When does this never happen to
When two objects interact (physical and field) they exert equal in magnetic and of the same type of force on each other but on different bodies and opposite in direction
Anything that’s the same object
Give example of you falling through earth in Newton’s third law
You falling Earth exerts a force of your weight on you but you exert a force of your weight as this is equal and opposite on the earth. Because earth do big, we don’t feel this
Where do forced of contact originate from
Electrostatic repulsion between electrons in atomic nuclei
Momentum equation
Momentum = mass x velocity
Vector
What is the principle of conservation of momentum
Learn
For a system of interacting objects, a closed system - the total momentum in a direction remains constant , as long as no external forces act upon it!
Why does a gun recoil when shoot?
The system of bodies has a momentum of 0 initially
- when shot, it still should have 0 momentum in total
- so gun goes back to provide negative momentum for bucket
How to investigate momentum
Use air tracks to reduce friction, or just a trolley
The. Use light gates to find out velocities
What makes a collision elastic vs in elastic
What is conserved both times tho
An elastic collision is when no kinetic energy is transferred to other forms when colliding , KE is conserved
An inelastic collision is when kE is transferred to other forms (such as in cars ineskstic, KE causes bumpers to crumple etc, sound etc)
Total energy is conserved both times
What is new Newton’s second law
The resultant force on a body is proportional to the rate of change of momentum in the same direction
F = change momentum / change in time
The k is removed by = to 1
Why do we need this equation instead of old f = ma
When can you use f=ma
This accounts for mass thst changes aswell, such as when going at speed of light, or when fuel runs out
When mass is constant
What is impulse
Impulse is just f x change in time
This = change of momentum
This is the area underneath a force time graph
Why are ideas of impulse used?
In reality to force applied to an object in an amount of time is never constant , fluctuations happen
That’s why you can analyse these using impulse , where force was highedt
What to remember when doing change in monemtum questions
To actuality fi final momentum - initial momentum
How to calculate momentum in two directions calculations,
Momentum is conserved, in ALL PLANES
So initial momentum = final momentum in x plane and y plane
So pick a plane and solve
What two conditions are needed for an elastic collision to happen?
- total kinetic energy is conserved
- SAME MASS,
If not same mass , according to 1/2 mv2 you will never have the same end velocity = momentum won’t be same or something
If these two are observed momentum is conserved and total energy too
What are examples of elastic and ineasltic collisosn
Elastic = ball this ball and ball stops other keeps moving at same speed
Ineakstic, ball hits ball and they both stop (energy gone to transform car) or slightly moves back
What is science behind seatbelts crumple zones etc ?
These slow the time it takes for momentum to be conserved
If f = momentum / time, and you INCREASE the time it takes for same momentum, then a less Fr is felt on you, so less likely to get damaged
Thus featured will try slow you down
Give example of featured for safety try to slow down
Crumple zones - deform which means it takes longer
- seatbelts
Air bags
How to describe motion of something after it has been hit ?
Use ideas of Moneten, like gun firing, it will go back and for same mass, lose velocity
How to describe motion with acceleration using f against t graph
As f= ma , if the resultant force decreases, so will acelerwtion
What about impulse, is this ever conserved!
Yes
Newton thrid law means in impact same force exerted
Time of contact dame
So imoukse same but opposite directions = conserved
Bruh what is momentum if bith ibjects started at 0
The same so net is 0 if it started that way
Why is momentum at 90° if something travelling horizontally gonna remain 0
As the component momentum in y plane is 0, end y plane has to be 0
