P2.2 Flashcards
What can forces do and what do they enable us to do
- change speed, direction and shape of objects
- allows objects to interact with each other
Contact vs non contact forces
Contact : normal, friction, air resistance, up thrust, tension etc
Non contact: magnetism, gravitational force, electrostatics
Newton third law of motion…
What are important about force parings?
‘For every action there is an equal and opposite reaction’
Forces come in pairs, but they act on different objects, allowing things to move and not always be stationary.
Key points
# forces act on different objects # forces are the same size and type (like gravitational ) (MAKE SURE THEY ARE SAME CONTACT OR NON CONTACT OR ELSE THEY ARENT’ PAIRS #forces act in opposite directions
How does a free body diagram show an equilibrium force
If all of them touch from nose to tail, like in a triangle or square…
What you need to remember about Free body diagrams compared to just showing all the forces on a diagram
Key thing you need to remember is a free body diagram shows all the forces acting only on that object, not say on the road or to the air as a result of resistance. That just helps explain and confirms Newton’s third law- that all forces have equal and opposite reaction but they act on different objects, which allows for a resultant force and thus for us to move…
Remember to resolve forces you
Draw them manually and use a scale, make nose touch tip and then you can see the vertical and horizontal components.
Newton first law is:
What does this mean about resultant forces
“An object will remain stationary or move with uniform velocity unless a force acts on it”
- This means that if there is no resultant force, and object is stationary, it remains stationary, but if object was moving already, it will move forever until a force acts on it. This isn’t possible on earth but without friction etc it is plausible.
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Newton second law + what is the equation?
A resultant force will produce an acceleration with equation FORCE= MASS X ACCELERATION.
Calculate RESULTANT FORCE
What happens is there is a resultant force + example of still car vs moving one
if there is a resultant force, then the object will accelerate in the direction of the force. This can take forms of stopping, starting, speeding up, slowing down and changing direction. Think of it like an object floating in uniform velocity in space because no resultant forces acting on it, but then gravitational force from an asteroid takes effect- now it accelerates by changing direction and speed etc,
A car is still at a parking bay. There is weight of car acting on the earth, and the normal force of the earth reacting on the car- which are equal and mean no resultant force, the car will continue to be still.
However if car is still but force applied via wheels- then resultant force present, and car will accelerate.
What does the acceleration of a resultant force in second law depend on?
The size of resultant force The mass (inertia how hard it is to change velocity of an object) of an object.
It is therefore inversely proportional to the inertial mass, but proportional to force…
What is inertia (relates ish to second law.) but why is the first law referred to as law of inertia
The inertia of an object is a measure of how difficult it is to change velocity, and explains why it is harder to move a hammer then feather. It is the tendency of an object to remain at rest or constant velocity, therefore first law…
Amount of inertia depends on mass of object , according to newton second law, mass = force over acceleration, therefore to move a higher mass at a certain acceleration you need more force…
PRACTICAL: how to show newton second law with a simple experiment
) set up two light gates and attach a trolley to some weights over a pulley that you will drop.
2) Program the distance of the flag at each light gate, and this will automatically calculate speeds and acceleration of the trolley, as it times how long it took for the trolley to get through both light gates .
3) increase mass, and plot a graph. You should get a straight line of force proportional to acceleration.
4) there is frictional forces, so to avoid this you can use an AIR TRACK which reduces friction.
If you change the experiment by keeping force constant but changing mass of trolley, then you would get inversely proportional curve thing
How is ISS constantly accelerations with a constant speed.
Where does the force should be aimed?
As it goes in circle, it’s direction is always changing, therefore it’s velocity is changing and so it accelerates. A force aimed at the centre is needed to do this.
MOMENTUM EQUATION
What is law of conversation of momentum?
Momentum (Kg m/s)= mass x velocity
Momentum is vector
Momentum1 + 2= momentum1 + 2, momentum is conserved
Make sure in calculations adding momentum’s to take in account for - velocity
Also make sure if asking for one object you use that object mass, if both then both.
Elastic vs I inelastic collision
Elastic= when all of if the energy in kinetic stores get transferred to each other, and none is lost
Inelastic = some of the kinetic energy gets transferred to surroundings, in practice this will happen all of the time, but momentum still conserved. Such as snooker ball hit other,energy transferred by sound.
