Scalars and Vectors Flashcards
What is a vector?
A quantity of unit and magnitude with direction
What is a scalar?
A quantity of unit and magnitude without direction
What is magnitude?
The size of something
What is the difference between distance and displacement?
Distance is how far an object has travelled but displacement is how far away an object is from where it started
When do you use a parallelogram of forces?
To find the resultant force acting on an object, when the two forces are working in different directions
How do you draw a parallelogram of forces?
Draw your line to scale
Find the angle in the question and draw the line to scale
Repeat on the other side but flipped
Draw from one side to the other and measure
Times the measurement by the scale to get the resultant force
What is a moment?
The turning effect of a pivot point
What is the pivot/ fulcrum?
The hinge or point of rotation
What is the equation for moment?
moment = perpendicular distance from force to point x force
M = d x f
Nm = M x N
What is equilibrium?
When the sum of the clockwise moment equals the sum of the anticlockwise moments. The moments are balanced and there is no overall turning effect
What is the centre of mass?
The point of an object at which is mass can be thought of is being concentrated
How to find the centre of mass of symmetrical objects
Mark the axis
Follow the lines to the centre of the object and mark the point
What is the suspension method?
Drill a small hole in the object and hang it up so that it is free to swing
hang a plum line- a piece of string with weight hanging on it from the same point this lets you mark the vertical line directly below this suspension point
drill another hole at a different location within the object
again hang the plum line to determine the vertical and market on the point of which the two marked line cross is the centre of mass
What is stopping distance?
how long it will take for an object to stop moving
What two parts make up the stopping distance of a car?
thinking distance and breaking distance
what is the thinking distance?
The distance travelled during the reaction time of the driver
what is the breaking distance?
The distance travelled while the brakes are applied
what is the formula for the stopping distance?
stopping distance = thinking distance + breaking distance
What’s the formula for the thinking distance?
thinking distance = initial velocity
x reaction time
What is terminal velocity?
This is reached when the air resistance from falling reaches the same force as the weight of the object falling so the speed reached a constant point
what is drag?
The force pushing on an object in the opposite direction of movement whilst it is in a liquid of gas
why is drag caused?
The object has to push away the particles
what things affect drag?
speed of object
Shape of object- wide and flat means more drag
Viscosity of liquid
What is momentum
The tendency of the object to keep moving in the same direction. It is difficult to change the direction of movement of an object with a lot of momentum
How does momentum work
The bigger the momentum of an object, the harder it is to stop that object moving. The momentum of an object depends on its mass and velocity
What is the formula for momentum
momentum = mass * velocity
P = m * v
What are the units of measurements for momentum
kgm/s
kilogram metres per second
Is momentum a scalar or vector?
Vector because it is a product of mass and velocity, velocity is a vector, so momentum is also a vector
How do you calculate the velocity of objects after a collision?
- Calculate the total momentum before collision: P = m x v for both objects and add them together
- Calculate the total mass: add them together
- Rearrange the equation for velocity: v = P/m
What is the equation for impact force?
force = change in momentum / time taken
How to reduce impact force?
Increase the time taken
Decrease the mass
Decrease the change in velocity - apply the brakes
Why do we work out the average impact force
Because the rate of deceleration will vary during collision
What is the formula for deceleration?
change in velocity / impact time
What is impact time?
How long it takes for a moving object to completely stop after a collision takes place
How do seatbelts save lives?
Seat belts increase the contact time by stretching the seat belt. This means the change in momentum stays constant, therefore the impact force is reduced.
What is Hookes law?
The extension of a spring is directly proportional to the force that is applied to it, provided the limit of proportionality is not reached
What is the formula for Hookes law?
Force = sprint constant x extension
F = ke
N = N/m x m
What is the spring constant dependant on?
The material of the spring and where the spring is places
What is the spring constant?
A measure of the stiffness of a spring or material. It is found from the gradient of a force extension graph
What are the units for spring constant?
Nm(-1) or newtons per metre
