P4 Flashcards
What is a contact force?
Forces that require the objects to be touching e.g. friction
What is a non-contact force?
Forces in which the objects aren’t touching e.g. gravity
What is Newtons third law?
When two objects interact, the forces they exert on each other are equal and opposite
Is a book sitting on a table an interaction pair?
No, there are 4 forces at work-
- The book being pulled down by gravity
- The book pulling up on the Earth
- The table pushing up on the book
- The book pushing down on the table
What is weight?
A downwards force due to gravitational attraction between an object and a planet
The gravitational field strength of Earth is around 10 N
You calculate weight by multiplying ones mass by 10
What are scalar quantities?
Just number (e.g. speed, distance, time etc)
What are vector quantities?
Numbers and direction (e.g. velocity, displacement etc)
What is acceleration?
The change in velocity over a certain amount of time
How can you work out average speed in a distance time graph?
Change in y / Change in x
What is accelerating and decelerating on a distance time graph?
Accelerating = gradient getting steeper Decelerating = gradient getting less steep
What axis is time always on?
The x
What is the gradient on a velocity time graph?
Average acceleration
What is the resultant force?
The overall force acting on a point or object
What is a freebody diagram?
A diagram in which you draw arrows in the direction forces are acting on an object, with the size of the force correlating with the size
How can you use scale diagrams to find resultant force?
0) Assign a scale for N (e.g. 1 cm = 1 N)
1) Draw all the forces acting on an object tip to tail
2) Draw a straight line from the start of the first line to the end of the last
3) Measure the length of the length of the line to find the magnitude of the resultant force, and measure the angle to find the direction of the resultant force
What does it mean if an object is in equilibrium?
When all the forces acting on it are balanced
What is Newtons first law?
If an object is moving in a straight line, and the resultant force is 0 N, it will carry on moving in a straight line at a constant speed
If an object is stationary and the resultant force is 0 N, it will not move
What is Newtons second law?
That a change of momentum due to a force, is proportional to the size of the force and the time for which it acts
Change of momentum (kg m/s) = Resultant force (N) x Time for which it acts (s)
What is the law of conservation of momentum?
In a collision where no external forces act, momentum does not change i.e after a collision the momentum is the same
What is inertial mass?
The measure of how difficult it is to change the velocity of the object
What is a moment?
The rotational effect of a force
How can you increase the turning effect?
Greater the applied force or further the force from the pivot
What do levers do?
Transfer the rotational effect of a force- push one end down and the rotation around the pivot causes the other to rise
They make doing tasks like lifting and moving easier
What do gears do?
They fit together and transfer the turning effect
How can you measure reaction time?
Ruler drop test
When is work done?
When a force moves an object, transferring energy
In a situation where there are no frictional forces, what does work done =
It will be = to the amount of energy transferred to useful stores
What is power?
The rate of energy transfer
