Forces & Motion Flashcards
What is distance
Distance is how far an object moved. It is a scalar quantity and does not include direction
What is displacement
Displacement is how far an object has travelled in a straight line from its starting point to its finishing point .it is a vector quantity and includes distance and direction
What is speed
-speed is how fast an object is moving with no regard for direction
Is the speed at which an object moves constant
The speed at which an object moves is rarely constant as the spped at which an object goes varies
What are factors affecting speed
Factors affecting speed are terrain,fitness and distance travelled
What are typical speeds of different transport methods
- Walking=1.5m/s
- running=3m/s
- cycling=6m/s
What other things also have varying speeds
- Wind and sound have varying speeds
- average speed of sound = 330m/s
What is the equation to work out distance travelled
Distance travelled(m)= speed x time
What is velocity
- Velocity is speed in a given direction
- Velocity is a vector quantity
Why can you have objects travelling at a constant speed but a changing velocity
You can have objects travelling at a constant spped but a changing velocity as an object (in a circle maybe) may be at a constant speed but at a changing velocity because of the changes of directions
What is acceleration
Acceleration is the change in velocity over a set period of time
What is the equation for acceleration
Acceleration(m/s2)= change in velocity divided by time
What is decceleration
Deceleration is just negative acceleration
How do you work out uniform acceleration
Final velocity^2-initial velocity^2 =2 acceleration x distance
What is friction
Friction is a force that acts between two surfaces when they are in contact . Friction always acts in the opposite direction to movement.
What is drag
Drag is the type of resistance you get in a fluid (liquid or gas) . Air resistance is a type of drag.
How is terminal velocity reacted
- At first when an object is falling the force of gravity acting on the object is much greater than the frictional force slowing it down ,so the object accelerates
- Then as the objects speed increases so does the frictional force acting against it. This gradually reduces the objects acceleration until eventually the accelerating force becomes equal the frictional force acting against it . This leads to a resultant force of 0 and the object has reached its terminal velocity
How does terminal velocity vary depening on air resistance
On earth air resistance causes objects to fall at different speeds .The terminal velocity of an object is determined by its drag in comparison to its weight. An object with a higher air resistance will reach its terminal velocity quicker than an object with a lower air resistance .
A skydiver for example without a parachute will have a small area and not much air resistance keeping him up meaning he will reach a high unsafe terminal velocity . Whereas a skydiver with a parachute will have the smae force pulling him down but a much larger area and therefore more air resistance .This means the terminal velocity will come much quicker and the skydiver will hit the ground at a safe speed.
What is newtons first law of motion
If the resultant force on a stationary object is zero the object will remain stationary
If the resultant force on a moving object is zero the object will carry on moving at the same velocity .
- This means when a vehicle is travelling the driving and resistive force must be balanced for the object to remain at a constant velocity
- Also the velocity of the object will only change if theres a non zero resultant force acting on the object
What is newtons second law of motion
Resultant force = mass x acceleration
-The larger the resultant force acting on an object the more it accelerates
They are directly proportional
-Mass and acceleration are inversely proportional, an object with a bigger mass will accelerate less
What is newtons third law of motion
When two objects interact they exert equal and opposite forces on each other
What is inertia
Inertia is the tendancy an objects motion to remain unchanged
E.g a train that is moving will continue to move unless acted upon by a resultant firce
What is an objects inertial mass
An objects inertial mass is how difficult it is to change that objects inertia
What is thinking distance
Thinking distance is how far a car travels during the time it takes the driver to react to a hazard on the road
What is braking distance
Braking distance is how far the car travels once the breaks have been applied
What is the equation to work out stopping distance
Stopping distance = thinking distance + braking distance
What are the factors that affect thinking distance
- Speed~ The faster the car is going the further the car will go in the time it takes the driver to react
- Reaction time~ The longer the reaction time ,the further the driver will travel after seeing the hazard (Reaction time affected by drugs and alchohol ) ( typical reaction time 0.2 -0.9 seconds)
What are the factors affecting braking distance
- Speed ~ the faster you are going the longer it takes the vehicle to stop
- Weather conditions-Icy or wet weather conditions cause there to be less grip between the tyres on the car and the road surface meaning the tyres could skid and cause an accident
- condition of tyres - If tyres are bald(have no thread left) they cannot get rid of water which could lead to skidding in wet weather conditions
- Condition of brakes~ If brakes are worn or faulty they will not be able to apply as much force as well maintained brakes which could be dangerous if you need to brake hard
Why do brakes heat up when they are pressed
When a brake pedal is pushed it causes brake pads to be pressed onto the wheels. This contact causes friction which causes energy to be transferred/work to be done . Energy is transferred from the kinetic energy store of the wheels to the thermal energy store of the brakes which causes them to heat up
Why can larger decelerations be dangerous
Large decelerations can be dangerous because great braking forces have to be applied in order to stop the car . These braking forces cause lots of energy to be transffered to the thermal energy store of the brakes which may causes the brakes to overheat and not work aswell . These large braking forces could also cause the car to skid
What is the equation to find momentum
Momentum(kg m/s) = mass(kg) x velocity (m/s)
The greater the mass or velocity of an object the more momentum it will have
What is the conservation of momentum
The conservation of momentum is momentum before an event= momentum after an event .
What is the equation including change in momentum
Force (N)=change in momentum(kg m/s)Divided by change in time (s)
If someones momentum changes very quickly the forces on the body will be very large and more likely to cause injury
Why are cars designed to slow people down
Cars are design to slow people down over a longer period of time so that they can maximise the amount of time in a crash so that the change in momentum is slower and there is an overall smaller force. Smaller force means that injuries are likely to be less severe
What are the safety features on a car
- Crumple zones- Crumple zones that crumple on impact,increasing the time taken for the car to stop
- Seat belts stretch slightly increasing the time taken for the wearer to stop
- Airbags-Airbags inflate before you hit the dashboard . The compressing air slows you down more gradually that hitting the hard dashboard
What are the safety implements on a helmet
A helmet has a crushable layer which increases the time taken for your head to crash against the floor therefore reducing severity of injuries
What are the safety features on crash mats
Crash mats increase the time taken for you to stop if you fall on them . This is because they are made from compressible squashy material
