Physics Unit 1

• A distance time graph has distance on the y axis (usually in metres) and time on the x axis (usually in seconds). The gradient of the line (change in y/ change in x) is the speed. If the line is flat then the object is stationary.
• average speed = distance moved/time taken
• Practical: investigate the motion of everyday objects such as a toy car or tennis ball. Apparatus: stop watch and metre rule. Mark the start and end positions for the know distance. Use a metre rule to measure the distance. Line up front of car with start point, release and start timer. Move eyes to end point. Stop timer when front of car passes end point. Improve by repeating and averaging. Make sure car starts from stationary. Calculate average speed using: average speed = distance travelled/ time taken.
• acceleration = change in velocity/time taken
• On a velocity time graph the velocity-time graph the velocity is on the y axis (usually in m/s) and time is on the x axis (usually in s). If the line is flat then the object is moving at a constant velocity. the gradient of the line is the acceleration. The area under the line is the distance travelled.  
• Gradient = acceleration= change in y/change in x = change in velocity/time.
• The area under the graph can be calculated as rectangles and triangles, or by counting boxes, is equal to the distance travelled. 
• v^2=u^2+2as. v= final speed. u= initial speed. a= acceleration. s= distance moved. (final speed)^2 = (initial speed)^2 + (2 x acceleration x distance moved).
• Forces can act on a body to change the velocity, so the speed, direction or both. Or forces can change the shape of a body, stretching it squishing it or twisting it. 
• Gravitational, weight, friction, electrostatic, air resistance (drag), tension (force in a spring), up thrust, lift, thrust.
• Scalars are quantities with only magnitude (size). Vectors are quantities with magnitude (size) and direction.
• Force has a magnitude measured in (N) but it also has a direction, a push or a pull, up, down, left or right. So force is a vector.  
• Friction is caused by surfaces rubbing. The force always acts in the opposite direction to motion.   
• force = mass x acceleration
• weight = mass x gravitational field strength
• Stopping distance = Thinking distance + Breaking distance 
• Thinking distance Affected by: Tiredness, Alcohol, speed of the car, Drugs (avoid as drugs can increase or decrease thinking distance).
• Braking distance affected by: Road conditions, Tire conditions, Brake conditions, speed of the car, mass of the car
• Initially the only force is weight as drag is proportional to velocity. So the object accelerates downwards. As it accelerates the velocity so the drag increases as well. meaning there is a smaller resultant force downwards so a smaller acceleration. Until the object reaches a speed where the drag is equal to the weight meaning there is no acceleration, this velocity is know as terminal velocity. 
• Practical investigate how extension varies with applied force for helical springs, metal wires and rubber bands.

  1. Attach your helical spring to the clamp stand.
  2. Measure the length of your spring against the ruler without any hanging masses.
  3. Hang a mass of 100g on the spring
  4. Measure the new length of the spring
  5. Calculate the extension of the spring
  6. Repeat steps 3-5 for increasing the mass in increments of 100g
  7. Take note of your results in the table.
• Hooke’s law is that extension is directly proportional to force applied. This is shown by the straight line on the force-extension graph. Hooke’s law is obeyed as long as the line is straight.   
• Elastic behaviour is the ability of a material to recover original shape after the force is removed. in a spring this occurs when the force is lower than the elastic limit. loading and unloading force extension curves can be different as long as it returns to its original shape. 
• momentum = mass x velocity. p = m x v.
• To reduce the force experienced by the passenger you need to extend the time for a passenger to stop in a collision. As force is the change in momentum divided by time.  
• force = change in momentum/time taken. F = (mv - mu)/t
• Every action has an equal and opposite reaction. Book pushes down on table, table pushes up on book. So book doesn’t accelerate. 

  Table pushes down on floor, floor pushes up on table. So table doesn’t accelerate. 
• moment = force x perpendicular distance from the pivot
• When moments are taken from the right hand side as the block is a greater distance the force from the left hand pivot must be bigger to counteract it. The opposite is true for the left hand side. 
• Weight of a body acts through its centre of gravity.
• The principle of moments states that when the clockwise moments are equal to the anticlockwise moments a body will be in equilibrium.