Physics p2

• Newton's First Law

  The velocity, speed, and/or direction of an object will only change if a resultant force is acting on it
• Newton's First Law

  1. If the resultant force on a stationary object is zero, the object will remain stationary

  2. If the resultant force on a moving object is zero, it will continue moving at the same velocity, in a straight line

  3. If the resultant force on an object is not zero, its velocity will change
• When a car is travelling at a steady speed, the resistive forces (e.g., friction and air resistance) must be balanced with the driving forces
• Changes in velocity

  • Starts to move
  • Stops moving
  • Speeds up
  • Slows down
  • Changes direction
• There must be a resultant force acting on an object if it is doing any of the things listed above
• Newton's Second Law

  The acceleration a of an object is proportional to the resultant force on the object and inversely proportional to the mass of the object
• Resultant force, mass, and acceleration are linked by the equation: resultant force (N) = mass (kg) x acceleration (m/s²)
• Newton's Third Law states that whenever two objects interact with each other, they exert equal and opposite forces on each other
• Forces always occur in pairs, each pair of forces act on separate objects, are the same size as each other, act in opposite directions along the same line, and are of the same type
• Stopping distance

  The distance it takes a body, such as a car, to stop is made up of thinking distance and braking distance
• Thinking distance

  The distance the vehicle travels during the driver's reaction time, proportional to the speed of the vehicle
• Braking distance

  The distance the vehicle travels once the brakes have been applied, not proportional to speed
• Speed has a bigger effect on braking distance than on thinking distance
• Reaction time

  The time it takes someone to respond to a stimulus, ranging from 0.25 to 0.95 seconds
• Factors affecting reaction time

  • Tiredness
  • Drugs
  • Alcohol
  • Distractions
• Braking distance

  Can be affected by the speed of the vehicle, road conditions, and the condition of brakes and tyres
• When the brakes of a vehicle are applied, a frictional force is applied to its wheel, transferring energy from the kinetic energy store of the car to the thermal energy stores of the brakes, increasing the temperature of the brakes
• The faster a vehicle moves or the greater its mass, the greater the amount of energy in its kinetic energy store, the more work that has to be done to transfer the energy to slow it down, the greater the braking force needed to stop it in a certain distance, and the greater the distance needed to stop it with a certain braking force
• Waves

  Waves transfer energy from one place to another without transferring matter, and may be transverse or longitudinal
• Mechanical waves

  Require a substance (a medium) to travel through, where the particles in the substance oscillate (vibrate) and pass energy on to neighbouring particles
• Transverse waves

  The oscillations are perpendicular (at right angles) to the direction of energy transfer
• Longitudinal waves

  The oscillations are parallel to the direction of energy transfer, causing particles in a substance to be squashed closer together and pulled further apart, producing areas of compression and rarefaction
• Wave equations

  When waves travel from one medium to another, their speed and wavelength may change but the frequency always stays the same
• Electromagnetic (EM) waves

  Transverse waves that transfer energy from their source to an absorber, forming a continuous spectrum grouped by wavelengths and frequencies
• EM waves all travel at a speed of 3 x 10^8 m/s through a vacuum
• EM waves of a wide range of frequencies can be absorbed or produced by changes inside an atom or nucleus
• Uses of EM waves

  • Radio waves
  • Microwaves
  • Infrared
  • Visible light
  • Ultraviolet
  • X-rays
  • Gamma rays
• Hazards of EM waves

  • UV can damage skin cells and cause blindness
  • X-rays and gamma rays are a form of ionising radiation that can damage or kill cells, cause mutation of genes, and lead to cancers
• Radiation dose (in sieverts) is the risk of harm from exposure of the body to a particular radiation
• Refraction of EM waves

  Ray diagrams show what happens when a wave is refracted (changes direction) at the boundary between two different substances
• Magnets

  Have a north (N) and a south (S) pole
• When two magnets are brought close together

  They exert a non-contact force on each other
• Repulsion

  • If the poles are the same (N and N or S and S), they will repel each other
• Attraction

  • If the poles are different (N and S or S and N), they will attract each other
• The force between a magnet and a magnetic material (iron, steel, cobalt, or nickel) is always attractive
• Magnetic field

  The region around a magnet where another magnet or magnetic material will experience a force due to the magnet
• Magnetic field lines

  • Show the direction of the force that would act on a north pole at that point
  • Always point from the north pole of a magnet to its south pole
• A magnetic field's strength

  • Is greatest at the poles and decreases as distance from the magnet increases
  • The closer together the field lines are, the stronger the field
• Permanent magnet

  Produces its own magnetic field which is always there
• Induced magnet

  An object that becomes magnetic when it is placed in a magnetic field