# physics 3

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• physics 3
• speed
• speed= distance/ time
• average speed= (u+v)/ 2
• u= start speed
• v= end speed
• acceleration
• speeding up is called acceleration, slowing down is called negative acceleration
• acceleration=change in speed/ time taken
• speed is just a number (magnitude) but velocity has a direction too. for example velocity = 30mph due north.
• mass and gravitational pull
• work done= force x distance
• when you put a book on a shelf, you are doing work on the book. the book gains gravitational potential energy, as it is moved away from he ground. the GPE of an object is the energy it has because of its position in the gravitational field, like the one around earth.
• change in GPE= mass x gravitational field strength (10) x change in height
• weight= mass x gravitational field strength (10)
• faces and motion
• force= mass x acceleration
• a lighter car is faster than a heavy one if they have the same engine power
• resultant force is the sum of all forces acting on an object, taking their direction into account.
• resultant force= thrust - frictional force
• stopping distances
• total stopping distance= thinking distance + breaking distance
• thinking distance is affected by different things
• tiredness
• drugs
• distractions
• speed.
• breaking distance has factors too
• speed
• conditions of brakes
• road and tyre conditions
• if too much force is applied to the wheel, it can lock and the car will skid.
• thinking distance and speed are directly proportional, however breaking distance has a squared relationship.
• power
• power is measured in watts (w), one joule is equal to one watt.
• power= work done/ time taken
• kinetic energy
• kinetic energy is produced by movement
• kinetic energy= 0.5 x mass x speed(to the power of 2)
• kinetic energy depends on
• mass of the object
• speed its traveling
• momentum
• momentum= mass x velocity
• the greater an objects mass or velocity the greater its momentum
• when the momentum of an object changes there is a force on the object that is given.
• force= change in momentum/ time
• if a change in momentum happens in a short time the force is large. using Newton's second law of motion, we can see that the deceleration of the object will also be high. if the change in momentum happens in a short time there will be large acceleration or deceleration, this is also requires large force.
• collisions & car safety
• in collisions the momentum changes suddenly, meaning a large force acts upon the vehicle and passengers
• safety features
• seat belts
• stretches using collision energy
• crumple zones
• uses collision energy to bend metal
• air bag
• uses collision energy to slowly force the gas into the air bag out and protects passenger's head.
• collapsible steering column
• collision energy is used to bend the steering column
• preventing accidents
• ABS (anti lock braking system
• helps drivers control the car. they can tell if the wheel is about to lock and reduce the pressure on the brake pads. then re apply it. ABS brakes pump on and off like this until the car stops. ABS reduces stopping distance.
• traction control
• condensates for any difference between the grid of the wheels on the road
• electric windows
• stops driver from being distracted by winding windows down via handle
• found around steering wheels, control radio or change gear, so drivers don't take their hands off the wheel.
• changing kinetic energy
• roller-coaters convert gravitational potential energy into kinetic energy
• change is GPE = change in kinetic energy
• mgh=0.5mv (to the power of 2)
• m=mass
• g= acceleration
• h= height
• v=speed
• it can be rearranged to give
• h= v(to the power of 2)/ 2g
• fuelling vehicles
• bio fuels also give off co2 but not in such high quantities
• electric cars store energy in large batteries, so they don't produce co2, however their batteries need to be charged by electricity from fossil fuels.
• fuel consumption depends on
• energy needed to increase kinetic energy
• greater mass = greater fuel consumption
• work done against resistive forces (friction ...)
• speed and driving style