Physics Topic 1- Motion and Forces

Physics Topic 1- Motion and Forces

1. Vector Quantities

   • Vector quantities have both magnitude and an associated direction
   • Examples of vector quantities
     • Force
     • Weight
     • Displacement
     • Velocity
     • Acceleration
     • Momentum

2. Motion

   • Speed= Distance/ Time
   • Speed measurement practicals
     • Ruler and stopwatch- Ruler measures distance travelled, stopwatch measures time taken
     • Light gates- Size of object measured with ruler, light gate connects to a timer which gives the reading
     • Video analysis- Distance moved from frame to frame observed on a ruler in the pictures, time between frames is known
   • Acceleration= change in velocity/ time taken
   • (final velocity) squared- (initial velocity) squared = 2 x acceleration x distance
   • An object will only accelerate if a resultant force acts on it
   • Gravitational attraction provides the centripetal force needed to keep a planet in orbit around the Sun

3. Scalar Quantites

   • Scalar quantities only have a magnitude or size
   • Examples of scalar quantities
     • Temperature
     • Mass
     • Energy
     • Distance
     • Speed
     • Density

4. Newtons Laws

   • First law of motion- an object remains in the same state of motion unless a resultant force acts on it
     • If the forces acting on an object are balanced, the resultant force is zero
   • Second law of motion- resultant force= mass x acceleration
     • The ratio of force over acceleration is called inertial mass. Inertial mass is a measure of how difficult it is to change the velocity of an object
     • Practical
   • Third law of motion- every action has an equal or opposite reaction
   • Weight= mass x gravitational field strength

5. Momentum

   • Momentum = mass x velocity
   • In a closed system (not affected by external forces) total momentum before an event = total momentum after an event
   • Force= change in momentum/ time taken

6. Motion of Vehicles

   • Stopping distance= thinking distance+ breaking distance
   • Reaction time- ruler drop test
   • When a force is applied to the breaks of a vehicle, there is work done by the friction between the breaks and the wheel. This reduces the kinetic energy of the vehicle.
   • Kinetic energy = 0.5 x mass x (velocity) squared
   • Work Done= Kinetic Energy

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