PHYSICS

• Force


  Can be exerted while in contact with an object or over a distance
• Forces that can act over a distance


  • Gravitational attraction of the Earth
  • Magnetic force
  • Electrostatic force
• Effects of a force


  • Can cause stationary objects to move
  • Can cause a moving object to move faster or slow down
  • Can cause a moving object to change direction or rotate
  • Can cause a temporary or permanent change in the shape of an object
• A set of forces acting on an object can be balanced and the object either remains at rest or continues to move at a constant velocity
• Weight (F)


  The force of gravitational attraction towards the Earth's centre
• Normal force (Fx)


  The force of the chair pushing up on the object
• Balanced forces are in equilibrium
• Drawing free body diagrams


  1. Draw a dot to represent the object

  2. Draw straight pencil lines with an arrow to represent the forces acting on the object and the direction in which they are acting

  3. Label the forces with an appropriate key
• Force


  Anything which changes or tends to change a body's state of equilibrium
• SI unit of force


  Newton (N)
• 1 N of force is approximately equal to the force exerted by the Earth's gravitational pull on a 100 g object on or near the Earth's surface
• Inertia


  The property of an object that causes it to resist a change to its state of motion
• Newton's First Law of Motion


  An object continues in a state of rest or uniform (moving with constant velocity) unless it is acted upon by a net or unbalanced force
• Smooth surface


  A surface which offers no resistance to a body moving on it
• Rough surface


  A surface which opposes the motion of a body on it
• Friction force (F)


  The resistance offered by a rough surface on a body, acting in a direction opposite to the motion
• Drag


  The friction force created when an object moves through air or water
• Tension (T)


  The force exerted by a taut string, cable, etc.
• Net force (F)


  The "left-over" force on a body after all the forces acting on the body have been taken into account, causing the body to accelerate
• Acceleration


  The rate of change of velocity
• The SI unit for velocity is the metre per second (m/s), therefore the change in velocity (Δv=v-u) divided by the change in time (Δt) results in a unit for acceleration as m/s²
• An electric current is a flow of charge
• Metallic conductors


  Substances that allow a flow of charge through them
• Metals conduct a flow of negative charge (electrons)
• Both positive and negative charges can move in conducting solutions or ionised gases
• Atoms


  Made up of positive protons, neutral neutrons and negative electrons
• Negatively charged object


  Has an excess of electrons
• Positively charged object


  Has a deficiency of electrons
• Electrons are either rubbed on or off an object, protons and neutrons do not move from the nucleus of an atom
• First law of electrostatics


  Like charges repel and unlike charges attract
• Cells


  Devices that convert chemical potential energy into electrical potential energy
• Ammeter


  Measures the rate of flow of charge, i.e. current strength
• Current strength (I)


  The amount of charge passing through a cross section of the conducting wire per unit time (per second)
• Resistor


  A device that opposes the flow of charge through it
• Potential difference (V)


  A measure of the work done per unit charge in moving from one point to another in a circuit
• Voltmeter


  Measures the potential difference between two points in a circuit, connected in parallel
• The more cells you add in series, the greater the total voltage, but they last only as long as one battery would
• The total voltage of the battery is divided up between all the resistors, in proportion to their resistance
• Current strength is the same at all points in a series circuit
• The more resistors there are in a series circuit, the greater the total resistance