P2a revision (part 1)

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juliasutton
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Page 1

Velocity Speed and Velocity are how fast you are going Measured in m/s, km/h or mph Speed is how fast you are going, no matter the direction Velocity is the same but a direction must be specified

Distance-time Graphs Gradient tells you the speed (Rise/run) Curves represent acceleration or deceleration Steepening curve means it's going up Levelling off curve shows it's slowing down

Acceleration How quickly velocity is changing this can be change in speed, direction or both Change in velocity is final velocity minus the original Measured in

Velocity-time Graphs Area under any section is equal to the distance travelled in that time interval A curve is changing acceleration Acceleration (at a sloping section is the gradient) When it is constant  just read it off the graph

Gravity Gravity is the force of Attraction between all masses Has 2 important effects On the surface of the planet, it makes all things accelerate towards the ground It gives everything a weight

Mass the amount of stuff in an object It's the same anywhere in the universe Not a force Measured in Kg

Weight Caused by the pull of gravitational forces Mostly the weight of an object is just the force of gravity pulling it towards the centre of the earth It is different depending on the strength of the gravitational forces A force measured in newtons Measured using a newton metre Measured in Newtons

On earth the gravitational strength is 10 N/kg

Resultant Forces The overall force on a point or object mostly there are two forces acting Overall force decides motion of the object If the forces act along the same line the overall force is found by adding or subtracting them If there is a resultant force acting on an object The object will change it's state of rest or motion It would change the object's velocity e.g A mug on a table Gravity is acting downwards Causes reaction force on the surface pushing up This makes it balance The resultant force would be 0 10N-10N=0N

Forces and Acceleration If the resultant force is 0 The object will stay stationary There has to be a resultant force to move If there is o resultant force on an object ti will carry on moving at the same velocity e.g. a car or train To move at a constant velocity the forces will be balanced If there is a resultant force (not 0) The object will accelerate in the direction of force This acceleration can be in 5 different forms 1. Starting 2. Stopping 3. Speeding up 4. slowing down 5. changing direction on a diagram the arrows will be unequal

Reaction Forces When 2 forces interact The forces they exert on each other are equal and opposite If you push on something the object will 'push back' twice as hard The 2 forces are acting on different objects The sized forces will be the same But the mass might be different and so there is an acceleration

Friction if there is not a force making it move Friction causes everything to slow down and stop Friction acts in the opposite direction to movement To travel at a steady speed the driving force need to balance the driving force  You get friction between 2 surfaces in contact Or when the object passes through a fluid

Resistance in Fluids mostly cause by air resistance or 'drag' This can be reduced by giving a streamline shape like sports cars Drag increases as speed increases At 70mph an engine has to wok harder than at 30mph to maintain a steady speed

Terminal Velocity Objects falling through fluids reach a terminal velocity when things start falling gravitational force is more than frictional forces So it accelerates So friction builds up This reduces acceleration Until they are equal It won't accelerate anymore It has reached its terminal velocity Depends on shape and area The accelerating force on falling objects is gravity It would make them fall at the same rate if it wasn't for air resistance Causes things to fall at different speeds Terminal velocity is determines by it's drag in comparison to its weight The frictional force depends on the shape and area e.g a skydiver Without parachute there is a small area and a force pulling him down He reaches a terminal velocity of about 120mph With the parachute there is more air resistance there is still the same force pulling him down The terminal velocity goes down to 15mph This is a safe speed

Stopping DistancesThinking Distance + Breaking Distance = Stopping DistancesThe total stopping distance is timed from when the driver first spots the hazard to when it stops

Thinking Distanceis affected by: How fast you're going - whatever reaction time the faster you re going the further you'll travel How alert you are - tired? Drugs? Alcohol? these all affect reaction time

Braking Distanceis affected by: How fast you're going - faster you're going the further it takes you to stop how good the brakes are - brakes must be checked and maintained, faulty brakes make it harder to stop quickly How good are the tyres - Must hve a dred depth of 1.6mm to be able to get rid of wayer in wet conditions. Stuff on road can make tyres skid How good is the grip - depends on road durface, weather conditions and tyres

Bad visibility and distractions don't help e.g. rain and plying with the radio Driver doesn't notice hazard Doesn't affect thinking distance it just means there is lees time to think and act Wet or icy roads make the stopping distance longer as prevent the tyres from getting grip and stopping quickly

Velocity and Acceleration

Gravity, weight and Mass

Acceleration and forces

Terminal velocity

Stopping Distances