P5 Flashcards
What is a vector quantity?
Have a magnitude and a direction
Examples of vector quantities?
Force Velocity Displacement Acceleration Momentum
What is a scalar quantity?
Only have a magnitude , no direction
Examples of scalar quantities
Speed Distance Time Temperature Mass
How are vectors usually represented?
Using an arrow, the length of the arrow shows the magnitude and the direction shows the direction of the quantity
What is a force?
A push or a pull on an object that is caused by interacting with something
What do all forces have to be?
Contact or non contact
What is a contact force?
Objects are physically touching
What is a non contact force?
Two objects dont need to be touching
Examples of contact forced?
Friction
Air resistance
Tension
Normal contact force
Examples of non contact forces?
Magnetic force
Gravitational force
Electrostatic force
What happens when two objects interact?
There is a force produced on both objects. The force is equal and opposite
Two important effects of gravity?
- on the surface of a planet, it pulls things towards the ground
- gives everything a weight
What is the mass of an object?
The amount of stuff within an object. The mass does not change .
What is the weight of an object?
Force acting on an object due to gravity (pull of the gravitational force on an object). It is caused by a gravitational field around the earth.
How does gravitational field strength vary?
Varies with location. Its stronger the closer you are to the mass causing the field , and stronger for larger massee.
What does the weight of an object depend on?
Strength of the gravitational field at the location of the object. The weight changes with a change of location.
What is weight measured in?
Newtons
What is gravitational field strength measured in?
Newtons per kilogram
What is the centre of mass of an object?
Single point on an object where the force (weight ) is acting. At the point you assume the whole mass is concentrated. For an object that has the same density throughout the shape , the point will be at the exact centre.
Is mass a force?
No
How is weight measured?
Using a calibrated spring balance(newtonmetre
How to work out the weight of an object?
Mass x gravitational field strength
How are mass and weight related?
They are directly proportional.
What is the resultant force?
If you have a number of forces acting at a single point , you can replace them with a single force. This force is called the resultant force. If they all act on the same line the overall effect is found by adding those going in the same direction and subtracting any going in the opposite direction
What is the work done ?
When a force causes an onject to move through a distance work is done on the object. So a force does work on an object when the force causes a displacement of the object
How to find the work done ?
Work done = force x distance
What does one joule equal to in netwon metres?
1
What happens when force moves an object through a distance?
Energy is transferred and work is done on the object..
What does the thing applying the force require?
A source of energy
What may happen if you apply a force to an object?
Stretch , compress or bend it
What do you need to stretch , compress or bend an object
Two forces acting on it . It can go back to its original shape.
What is an elastic object?
An object that can be elastically deformed
What is an inelastically formed object?
Doesnet return to its orignial shape after force has been removed
How is work done when an object is stretched or compressed?
Causes energy to be transferred to the elastic potential energy store of the object. If it is elastically deformed , all energy is transferred to the objects elastic potential energy.
How is extension and force related?
They are directly proportional , to a certain degree of proportionality ( if this is exceeded the object will break)
How to show force and extension are directly proportional ?
As you add more weight , the elastic potential energy increases.
How to work out the force using extension?
Force = spring constant x extension
What is the limit of proportionality?
Maximum force that can be on an extension
How to work out the elastic potential energy?
Elastic potential energy= 0.5 x spring constant x extension^2
How can a resultant force be worked out?
Single force can be resolved into two components at right angles to each other . Two components forces together have the same effect as a single force
What is the distance?
How far an object moves. It is a scalar quanitty
What is displacement?
Vector quantity , it measured the distance and direction in a straight line from an objects starting point to its finishing point. If you walk 5 m north then 5 m south , the displacement is 0 and the 10 m is the distance
What is speed compared to velocity ?
Speed is how fast you’re going and is a scalar quantity. Velocity is speed in a given direction , it is a vector quantity. speed is rarely constant , the speed when walking running or traveling in a car is constantly chnaging
How to find the speed of an object?
Speed = distance /time
Typical speed of a person walking?
1.5 m/s
Typical speed of running?
3 m/s
Typical speed of cycling?
6 m/s
What does speed a person can move depend on?
Terrain
Age
Fitness
Distance travelled
What effects the speed of sound?
What sound waves it travels through
What is the speed pf sound?
330 m/s
How does the speed of wind vary?
Due to temperature , atmospheric pressure and large buildings being in the proximity
How to calculate the distance travelled when an object moves at a constant speed?
Distance travelled = speed x time
What happens when an object moves in circle at a constant speed?
Has a constantly changing velocity , as the direction is always changing. Still a constant speed though.
What is acceleration?
The change in velocity in a certain amount of time
How to find the acceleration?
Acceleration = change in velocity / time
What is a deceleration?
A negative acceleration, an object that is slowing down
What unit has acceleration got?
M/s^2
What is uniform acceleration
A constant acceleration . Acceleration due to gravity is uniform for objects to fall
How to work out uniform velocity?
Final velocity^2 - initial velocity^2 = 2 x acceleration x distance
How on a velocity time graph can you find the acceleration?
Calculateinh gradient of line
How to work out the distance in a velocity time graph?
Find area under the graph
What is the acceleration of an object falling freely under gravity ?
9.8 m/s
What happens as a object moved through a fluid?
It initially accelerates due to the force of gravity . Eventually the resultant force will be zero and the object will move at its terminal velocity
What will happen to an object if not force is propelling it along?
It will eventually stop as friction is working against it , unless its in space
How does friction always work?
In the opposite direction to the movmentt
What is friction?
Movement of two surface in contact or when an object moves through a fluid, reduce friction with a lubricant
What is drag?
Resistance you get by a fluid . Air resistance is a type of drag
How to reduce drag?
Keeping the shape of an object streamlined , so the object is designed to allow fluid to flow easily across it, reducing drag
What will happen to an object if not force is propelling it along?
It will eventually stop as friction is working against it , unless its in space
What is terminal velocity?
When an object falls gravity is much more than the frictional force slowing it down , so it accelerates. As the speed increases friction builds up, which gradually reduced the acceleration until the frictional force is equal to the accelerating force. It will have reached its maximum speed, which is the terminal velocity, so will fall at a steady speed.
What effects the terminal veloctiy?
How streamlined the object is. Object with larger surface areas tend to have lower velocities
What is newtons first law?
If the resultant force on a stationary object is 0 , the object will remain stationary. If the resultant force on a moving object is 0 , it’ll just carry on moving at the same velocity(same speed and direction)
What doe newtons first law mean for a vehicle travelling at a steady speed?
The resistive and driving forces on the object are balanced. The velocity will only change if theres a non zero force resultant force acting on the object
What is newtons second law?
The acceleration of an object is proportional to the resultant force acting on the object , and inversely proportional to the mass of the object.
Equation for resultant force(newtons second law)?
Resuktsnt force = mass x acceleration
What is inertia?
Until acted upon by a resultsnt force , objects stay at rest and objects moving at a steady speed will stay moving at a steady speed. The tendency to continue in the same state of motion is called inertia
What is an objects inertial mass?
Measures how difficult it is to change the velocity of an object
How to calculate inertial mass?
Can be found using f=ma. Rearrange it so m= F/a, so the inertial mass is the ratio of force over acceleration.
What is newtons third law?
When two objects interact , the forced they exert are equal and opposite
Example of newtons third law?
If you push something, it will push back against you just as hard , and when you stop pushing so does that object
Why is an object in its equilibrium not newtons third law?
It has to be the same forces acting upon the object , it cannot be gravity and push, it has to be push and push
What is momentum?
the quantity of motion of a moving body, measured as a product of its mass and velocity. It is the impetus of an object.
How to work out momentum?
Momentum = mass x velocity
What is the total momentum in a closed system?
Before an event is equal to the total momentum after the event
How momentum works in collisions?
When balls collide in snooker , they are the exact same mass and size. Each collision is an event where the momentum is the same after the event.
If the red ball is stationary it has 0 momentum, the white ball is moving so it has a velocity. The white ball hits the red ball causing it to move. The white ball continues to move , but at a smaller velocity. The combined momentum of the red and white ball is equal to the original momentum of the white ball.
What is the stopping distance in a vehicle?
Sum of the distance the vehicle travels during the drivers reaction time (thinking distance) and the distance it travels under the braking force (braking distance). For a given braking force the greater the speed of the vehicle, the greater the stopping distance
What is the typical values for reaction times?
Between 0.2s and 0.9 seconds
What effects the drivers reaction times?
- tiredness
- drugs and alcohol
- distractions
How to measure reaction times?
Do a ruler drop test
What can effect the braking distance?
- poor vehicles conditions
- adverse road and weather conditions
What are adverse weather conditions and poor vehicle conditions?
Include wet or icy conditions. Poor vehcile conditins include problems with brakes or tires
What happens when force is applied to the brakes of a vehicle?
Work is done by the friction force between the brakes and the wheels reduce the kinetic energy of the vehicle and the temperature of the brakes increases.
What does the greater the speed mean for braking force?
Greater the speed means greater the breaking force needed to stop the vehicle in a certain distance
What does the greater the braking force mean?
The greater the deceleration of the vehicle. Large decelerations may lead to brake overheating and or loosing control
