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P1.1 - Motion/Forces
Motion/Forces In Action - OCR AS Physics
| Question | Answer |
|---|---|
| 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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