Physics 5 Flashcards
What is velocity ?
How fast you are going with a direction
What is speed ?
How fast something is going
On a distance time graph what is the gradient ?
Speed
What does a flat section mean on a distance time graph ?
Stationary
If a distance-time graph goes downwards, what is happening ?
Going back to starting point
What do curves represent on a distance-time graph ?
Acceleration or deceleration
How do you work out the speed with a distance-time graph ?
Vertical line
______________
Horizontal line
What is acceleration ?
How quickly the velocity is changing , it can be a change in speed, direction or both
Acceleration = ???
Change in velocity
_________________
Time taken
On a velocity time graph, what does a curve or diagonal line mean ?
Increasing / decreasing acceleration
What does a straight horizontal line represent on a velocity time graph ?
A steady speed
How can you find the acceleration on a velocity-time graph ?
Work out the gradient by dividing the vertical change by horizontal change
What is gravitational force ?
The force of attraction between all masses
What are two important effects of gravitational force ?
- It makes all things accelerate towards the ground
* It gives everything a weight
Are mass and weight the same thing ?
No
What is mass ?
The amount of ‘stuff’ in an object, this will be the same even when gravitational force changes
What is weight ?
It is determined by the strength of the gravitational force
What are weight and mass measured in ?
Weight - newtons
Mass - Kg
What formula relates mass and weight ?
Weight = mass x gravitational field strength
What is resultant force ?
The overall force on a point or object
What does resultant force determine ?
motion, whether acceleration deceleration or stay at a steady speed
What happens If the resultant force is zero, when the object is stationary ?
It will remain stationary
What happens if there is no resultant force on a moving object ?
It will continue to move at that velocity
What is the equation for a non-zero resultant force ?
F = m x a
Resultant force=massxacceleration
When two objects interact two forces are exerted, what are they ?
Equal and opposite
If the forces are always equal, how do things move ?
Even though the same force is exerted from each object, the forces are acting on different objects. One of the objects could be lighter than the other an therefore move
What does friction do ?
Slow things down
Why do objects come to a halt gradually when no force is propelling it ?
Because friction always acts in the opposite direction to movement
What is drag ?
Resistance from liquids or gases
What makes things less affected by drag ?
Being more streamlined
True or False - drag always says the same, even when the speed is increased
False, drag increases as speed increases
How does terminal velocity occur in fluids (liquids and gases) ?
When and object first begins to fall, gravity is greater than drag, so it accelerates. As the speed increases the drag increases, this gradually reduces the acceleration. Eventually it will no longer accelerate because friction and drag are equal.
What is stopping distance ?
The distance covered between a driver recognising a hazard and the vehicle coming to a halt
What two factors affect stopping distance ?
Thinking distance and breaking distance
Thinking distance is affected by what ?
- Speed - if you’re going fast then you’ll go further
* How alert you are - bad visibility or being tired can affect this
What affects breaking distance ?
- Speed
- How good your brakes are
- How good your tyres are
- How goo the grip is
What is work done ?
When a force moves an object, energy is transferred
Work done = ?
Force x Distance
Gravitational potential energy = ?
Mass x force of gravity x height
Kinetic energy = ?
1/2 x Mass x Speed^2
Is kinetic energy just speed ?
No it is the measure of mass and speed. A heavy Lorry at a high speed has more kinetic energy than a car of the same speed
What is the law of conservation of energy ?
Energy can never be made or destroyed, only converted into different forms.
If a car has kinetic energy, because it is moving, how does it lose this energy to stop moving ?
The kinetic energy has to be converted to heat energy as friction between the wheels and brake pads
When an object falls the potential energy is converted into what ?
Kinetic energy - this is why the further it falls the faster it goes
If work is done to change an elastic object’s shape, what is the energy converted into ?
Elastic potential energy, which is then converted into kinetic energy when the object returns to it’s original shape
What does the formula ‘F = k x e’ work out ? And what do k and e represent ?
The force needed to extend an elastic object. k represents the spring constant, which varies depending on the object. e is the extension
What is power ?
The rate of work being done, a more powerful object transfers a lot of energy in a short time
What is the formula for working out power ?
Power = work done divided by time taken
What is power measured in ?
Watts
One watt is equivalent to what ?
One joule of energy transferred per second
Momentum = ?
Mass x Velocity
What is the conservation of momentum ?
The rule that the momentum before an event (like a collision) and the momentum after are equal. This is only in a closed system
What is a closed system ?
When there are no external forces acting
Why do cars make the change in momentum longer with seat belts and airbags ?
Forces cause change in momentum. During a car crash, the passenger’s momentum changes very quickly so the forces on the body will be large. By reducing this momentum time the injury is also reduced
What are regenerative brakes ?
It acts as a generator, converting the kinetic energy into electrical energy which can be reused. Normal breaks convert kinetic energy to heat energy
