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# P1.1 - Motion/Forces

### Motion/Forces In Action - OCR AS Physics

What is the difference between Scalars and Vectors? Scalars only have magnitude, vectors have magnitude and direction.
How do you resolve vectors? Draw them tip to tail, then draw a resultant line. Work out the magnitude of the resultant using Pythagoras.
What equation do you get from 'acceleration is the rate of change of velocity'? v = u + at
What equation do you get from 's = average velocity x time'? s = (u + v)/2 x t
Define free fall: The motion of an object undergoing an acceleration of 'g'.
How do you calculate 'g'? The ball bearing experiment.
What did Aristotle say about heavy and light objects (he was wrong)? Heavier objects fall quicker than lighter objects. He got to this conclusion using reasoning.
What did Galileo say about heavy and light objects (he was correct)? All objects in free fall accelerate uniformly. He reckoned that the reason they don't in real-life is due to air resistance.
How did Galileo test his theory? He rolled a ball down an inclined plane, and measured the time taken.
If an object is accelerating, what does the displacement-time graph look like? It is curved.
What does the gradient of a displacement-time graph tell you? The velocity.
What does the gradient of a velocity-time graph tell you? The acceleration.
What does the area under a speed-time graph tell you? The distance travelled.
What is Newton's first law? An object will move in a straight line or stay still unless acted upon by an external force.
What is Newton's second law? Acceleration is proportional to the rate of change of momentum.
What does friction oppose? Motion.
What does friction convert kinetic energy into? Heat.
What does it mean when an object is at terminal velocity? The friction force equals the driving force. The resultant force = 0
How do you work out density? Mass/Volume
Where is the centre of gravity of an object? The single point that the entire weight of the object appears to act.
How do you determine the centre of gravity of an object? Hang the object freely from a point, hang a string on a bob from the point of suspension. Draw a line following the string. Hang the object from another point, repeat. The COG is where the lines cross.
If an object has a low centre of gravity, what does this mean? The object is stable.
What is a moment? The turning effect of a force.
How do you work out the moment of a force? moment = force x perpendicular distance from the pivot.
If moments are unbalanced, what does this mean? The object will turn.
What is a couple? A pair of forces of equal size, that act parallel to each other but in opposite directions.
How do you work out the torque of a couple? Torque = Size of one of the forces x perpendicular distance between them
What is the braking distance? The distance travelled from the moment the brakes are pressed to the car coming to a stop.
What is the thinking distance? The distance travelled from seeing the obstruction, to pressing the brake.
What is the stopping distance? Braking distance + thinking distance
name some car safety features: Seatbelts, airbags, crumple zones.
How do airbags make a car safer? They slow the person down over a longer period of time. This means that the force on them is less due to F = (v-u)/t
How do seat belts make a car safer? They stop the person hitting the steering wheel or going through the windscreen. They also give a little to slow the person down over a longer period of time.
How are airbags triggered? By a rapid deceleration. The car's accelerometer changes capacitance during a rapid deceleration which is detected by the computer. This kicks of a chemical reaction to inflate the airbag.
What is Trilateration? The user of three satellites to locate your position. This is calculated by seeing where the three spheres from the satellite cross.
Created by: vahajuddin

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