1. Speed
1.1. The distance travelled by an object per unit time
1.2. Average speed = total distance/ time taken
1.3. Scalar quantity
2. Velocity
2.1. Velocity of a body is uniform or constant if it moves with a steady speed in a straight line
2.2. Velocity = displacement / time taken = distance moved in a stated direction / time taken
2.3. Vector quantity
3. Acceleration
3.1. Rate of change of an object’s velocity
3.2. An object accelerates if its velocity changes
3.3. = change in velocity / time taken for change = (v-u)/t
3.4. Increase in velocity = positive acceleration
3.5. Decrease in velocity = negative acceleration = deceleration = retardation
3.6. Unit = ms^-2
3.7. Equations for Uniform Acceleration:
3.7.1. v = u + at = final velocity
3.7.2. Avg. velocity = a = s/t = (u+v)/2 or distance = s = (u+v)/2 *t
3.7.3. S = ut + (at^2)/2
3.7.4. v^2 = u^2 + 2as
4. Timers (useful for analysing motion in the laboratory)
4.1. Motion Sensors:
4.1.1. use the ultrasonic echo technique to determine the distance of an object from the sensor.
4.1.2. Connection with data logger and computer enables us to:
4.1.2.1. Distance-time graph
4.1.2.1.1. speed= distance/time
4.1.2.1.2. Slope or gradient represents speed/velocity of the body
4.1.2.1.3. Steeper slope = greater velocity
4.1.2.2. Velocity-time graph
4.1.2.2.1. area under a velocity–time graph measures the distance travelled.
4.1.2.2.2. When calculating the area from the graph, the unit of time must be the same on both axes
4.1.2.2.3. distance = average velocity × time = shaded area under the graph
4.1.2.2.4. slope or gradient of a velocity–time graph represents the acceleration of the body
4.2. Ticker Tape timer: tape charts
4.2.1. enables us to measure speeds and hence accelerations
4.2.2. a marker that vibrates 50 times a second and makes dots at 1/50s intervals on the paper tape being pulled through it; 1/50s is called a ‘tick’
4.2.3. distance between successive dots equals the average speed of an object per 1/50s
4.2.4. (consider the distance between two dots as ‘x’ cm: avg. speed = x cm /(1/50s))
4.2.5. ‘Tentick’ = 1/5s
4.2.6. Tape Charts:
4.2.6.1. made by sticking successive strips of tape, usually tentick lengths, side by side
4.3. Light gates/ Photogate timer:
4.3.1. Used to record the time taken for a trolley to pass through the gate
4.3.1.1. Light gates/photogate timers measure the motion of light through laminated particles and provide readings for time and other desired variables.
5. Falling Bodies
5.1. Acceleration of free fall is caused by the pull of Earth’s gravity = 9.8 m/s2
5.2. Rising bodies are decelerating
5.3. Air resistance or drag is the force of friction when an object moves through air or water
5.3.1. Has greater effect on lighter bodies
5.3.2. When falling downwards, air resistance increases with speed, reducing acceleration
5.4. terminal velocity
5.4.1. When Air resistance = weight
5.4.2. Object falls at constant velocity/steady rate
6. Forces
6.1. Force: action of one body on another, causing its velocity to change
6.2. Forces has magnitude and direction
6.3. Unit = Newton(force required to give mass of 1kg acceleration of 1m/s2)
6.4. Resultant force = single force that has the same effect as two or more forces
6.5. Balanced force when FR = 0 (if object has constant speed or is at rest)
6.6. Friction = force that opposes motion
6.6.1. Can be a help or hindrance
6.6.2. Results in heating
6.6.3. static/starting friction > sliding/dynamic friction > rolling friction
6.7. Scalars are added by ordinary arithmetic; vectors are added geometrically, taking account of their directions as well as their magnitudes
6.8. Parallelogram method
6.8.1. If two forces acting at a point are represented in size and direction by the sides of a parallelogram drawn from the point, their resultant is represented in size and direction by the diagonal of the parallelogram drawn from the point.
6.9. F = ma = force = mass*acceleration
6.9.1. Greater the mass of an object, smaller the acceleration it is given by a particular force
7. Newton's Laws
7.1. A body stays at rest, or if moving it continues to move with uniform velocity, unless an external force makes it behave differently.
7.1.1. All matter has inertia = matter has a built-in opposition to being moved if it is at rest or, if it is moving, to having its motion changed
7.1.2. Mass is the measure of inertia
7.2. F ∝ rate of change of momentum
7.2.1. Momentum = quantity of motion in a body
7.2.1.1. Unit = kgm/s or gcm/s
7.2.1.2. mass*velocity
7.2.1.3. Change in momentum = mv-mu = mass*final velocity - mass*initial velocity
7.2.1.4. Impulse = force* time for which it acts
7.2.1.5. Change in momentum = impulse force
7.2.1.6. Impulse equation → Ft = mv- mu → F = m(v-u) / t
7.2.1.7. Because a= v-u / t → F = m*a