Physics 2019 Yr 11 Flashcards
Distance
The distance between 2 points is how far they are apart
Displacement
Is the distance between 2 points in a specified direction
Speed
Is the rate at which distance changes with time
Speed = d/t
Av speed = tot distance/ tot time taken
Velocity
Is the rate of change of displacement with time
Velocity = displacement/ time unit m/s
Av velocity = (initial speed + final speed) / 2
Average speed
Is the total distance travelled divided by the total time taken
Av speed = tot distance/ tot time
Average velocity
Initial speed+ final speed / 2
Acceleration
Is the rate of change of velocity with time
A= change in velocity/time taken
Average speed
Is the total distance travelled divided by the total time taken
Av speed = tot distance/ tot time
Scalar
Is a physical quantity that has a magnitude but not direction
Eg distance, speed, rate of change of speed and time
Vector
Is a physical quantity that has both magnitude and direction
Eg displacement, velocity, acceleration and force
Balanced forces
When the forces exerted on an object are of equal size but acting in different (opposite) directions, then the forces are known as -balanced forces-
Unbalanced forces
When the forces applied to an object are unequal in size then the forces are known as -unbalanced forces-
Force measured in ?
Neutons
Springs
When a force is applied to a spring e.g hanging slotted masses on it, the spring will stretch. We usually call the amount it has stretched the EXTENSION. The relationship between the force applied to the spring and the extension is given by HOOKES LAW
Spring hookes law
Up to the limit of proportionality the extension of a helical spring is directly proportional to the applied load
Law is only true if the spring is not stretched beyond the LIMIT OF PROPORTIONALITY
A spring stretched beyond is ELASTIC LIMIT will not return to its original length and it has been permanently stretched
F=ke
Force = force K = spring constant E = extension
Force extension graph
The gradient of a force extension graph is equivalent to the print constant
Another useful way of writing hookes law
F1 over F2
E1 over E2
Turning effect or moment of a force
Turning effect of a force is called the moment and the point at which the object is fixed is called the moment. The size of the turning effect or moment depends of the size of the force and the distance between the force and the pivot
Principle of moments (law of the lever)
The principle of moments tells us about what happens when a lever with several forces acting on it is balanced or in equilibrium
Moment =
M = force x distance (perpendicular distance form pivot)
Reaction force
The reaction force acts through the pivot and does not create a Turing effect
Reaction force at pivot = acm force + cm force
Conditions for equilibrium
Clockwise moment about pivot = anti-clockwise moment about pivot
There must be no resultant or unbalanced force in any direction
Levers
Effort = (input) force Load = (output) force Furst class Scissors Seesaw Second class Nut cracker Wheel barrow Third class Tweezers Fishing rod
Centre of gravity
All points of an object are pulled toward the centre of gravity. It is a reg shale such as a rectangular block the centre of gravity will be at the very centre of the object.
Centre of mass
The centre of mass of an object is the point where its total mass appears to act. Unless an object is very large the centre of mass and the centre of gravity will be at the same point
How to find the c of g of a lever
The centre of gravity of a metre ruler is located at its midpoint 50cm u can also use this to work out the weight of the ruler without weighing it
Hand ruler on retort stand, make the pivot anywhere except the 59cm mark and hang 2N on the shorter side. Move until the metre stick is in equilibrium (balanced).
The moment produced by the 2N is now the same as the moment produced by the weight of the stick actingat the 50cm mark
What factors affect the stability of an object
The position of the centre of gravity of an object affects whether or not it will topple easily
The weight of an object acts vertically downwards from its centre of gravity. The object will topple when the line of action of this force (the weight) falls outside its base or to the outside of the toppling edge.
If the line of action of the force falls inside the base then the object will be stable and returns to its original position. The stability can therefore be increased by lowering the centre of gravity of an object
Widening the base
Pressure
Pressure is the force exerted per m squared
The amount of pressure depends on the size of the force and on the area over which the force acts. The smaller the area the greater the pressure. And the other way round
We can define pressure as
Force applied per unit surface area Newton’s per metre squared (N/ m2(squared))
The unit of pressure is the pascal
1Pa= 1N/msquared
Equation for pressure
P = F / A F = P x A A = F/P
What is the area under a speed time graph
The distance travelled
