Mod 3

• Average Speed equation: average speed = distance travelled/time taken
• What does a straight, sloping line represent in a distance/time graph? An object moving at a constant speed
• What is instantaneous speed? Speed over a very short period of time
• How do you find instantaneous speed? Drawing a tangent to a distance/time graph
• Average velocity equation: average velocity=change in displacement/time taken
• Displacement definition: The distance travelled in a particular direction - it is a vector with magnitude and direction
• Velocity definition: A vector quantity equal to the rate of change of displacement
• Acceleration definition: The rate of change of velocity
• Acceleration equation: acceleration=change in velocity/change in time
• What does the gradient of a velocity/time graph show? acceleration
• What does a straight horizontal line on a velocity/time graph represent?

  constant velocity - zero acceleration
• What is thinking distance? The distance travelled between the moment when you first see a reason to stop, to the moment when you use the brake
• What is braking distance?

  The distance travelled from the time the brake is applied until the vehicle stops
• Thinking distance equation: Thinking distance=speed x reaction time
• What does 'g' stand for? 'g' is the acceleration of free fall, 9.81ms-2
• Why is horizontal velocity constant? g cos 90 = 0
• Why does vertical velocity change? acceleration of free fall
• Define a Newton: A force of 1 Newton will give an object of 1kg an acceleration of 1ms-2 in the direction of the force
• Equation linking force, mass and acceleration: F=ma
• Units of a Newton: N (kg m s-2)
• Define weight: The gravitational force acting on an object with mass
• What instrument is used to measure force? A newtonmeter
• Define centre of mass: The point through which an external force will create straight line motion with no rotation
• Define centre of gravity: The imaginary point through which the entire weight of an object appears to act
• On a smooth, inclined slope, which equation gives the force acting parallel to the slope? mg sin 0
• On a smooth, inclined slope, which equation gives the force acting perpendicular to the slope? mg cos 0
• On a smooth, inclined slope, what is the name of the force acting upwards, perpendicular to the slope? Normal Reaction Force
• What is a drag force? A frictional force opposing the motion of an object in a fluid
• What is air resistance? Drag experienced by objects moving in air
• Which two factors affect drag force the most? Speed and cross sectional area
• What is terminal velocity?

  when the drag force on the object is equal and opposite to the weight
• what is the moment of a force?

  It is the turning effect of a force about some axis or point
• Equation for finding a moment: moment=force x perpendicular distance of the line of action of force from the axis or point of rotation
• What is the unit of a moment? Nm
• What is the principle of moments?

  For a body in rotational equillibrium, the sum of the anticlockwise moments about any point is equal to the sum of the clockwise moments about that same point
• What is a couple?

  A pair of equal and opposite forces applied to an object, which are parallel and along different lines
• What is a torque: The moment of a couple
• Equation to find a torque: torque of a couple=one of the forces x perpendicular separation between the forces
• What is density?

  mass per unit volume, p=m/v
• What are the units of density: kgm-3