Physics

• Convex lens reflect parallel rays of light inwards to a single point
• Convex lens cause light rays to converge at a principal focus
• Concave lens reflect parallel rays of light outwards from a principal focus
• Shortening the focal length makes the lens more powerful and refracts light strongly. A lens can also be made stronger by changing the shape or material
• Images are formed at points where all the light rays from a particular point on an object appear to come together
• Virtual image: light rays dont come together where the image appears to be
• hotter objects radiate more infrared in a given time
• Objects at a constant temperature emit infrared radiation at the same rate they absorb it
• As the altitude increases the atmosphere gets less dense, so there are fewer air molecules that collide with the surface
• In ultrasound, waves are partially reflected and refracted
• Ultrasound is used in industrial imaging, crack causes early reflection of waves. reflected waves can reach a detector and measure how far away the boundary is
• The more optically dense a material is the slower light will travel and the more it will bend towards the normal
• Measuring the Speed of Sound:

  1. set oscilloscope so 2 seperate waves
  2. align microphones 1 wavelength apart
  3. signal generator at set frequency
  4. measure wavelength
  5. measure wavespeed
• Measuring Water Waves:

  1. signal generator attatched to a dipper
  2. turn on lamp so crests can be projected on a screen below
  3. measure 10 wavelengths
• String Waves:

  1. signal generator should produce clear waves
• EM waves are produced by changes in atoms or nuclei, which is why atoms can absorb a variety of frequencies
• Refraction depends on wavespeed and the properties of the material. It changes wavelength but not frequency
• Reflection depends on wavelength
• Diffuse reflection occurs because all the normals are different
• Contact forces: tension, friction, normal contact force

  Non-contact force: magnetic, electrostatic, gravitational
• Interaction Pair: pair of equal and opposite forces that act on two interacting objects
• Weight is measured with a calibrated spring balance or newtonmeter. Mass and weight are directly proportional
• If a resultant force moves an object, work is done, transferring energy between stores
• Stretching, Compressing or Bending transfers energy and you need more than one force applied to change shape. The limit of proportionality is the maximum force above which the graph curves
• Link between Force and Extension:

  1. calculate weight of each mass
  2. measure natural length of the spring at eye level and add a marker to the bottom
  3. add a mass to the spring and allow it to come to rest. measure change in length
  4. repeat until you have 6 measurements and plot graph
• Levers increase distance from the pivot at which the force is applied
• Gears have teeth that interlock so that turning one causes another to turn in the opposite direction, so they can be used to transmit moments from one place to another. A force transmitted to a larger gear will be greater because of a greater distance to the pivot but it will turn slower
• pressure= height * density * gravitational field strength
• When an object is submerged pressure exerts a force on it from every direction. Because pressure increases with depth, the force exerted on the bottom of the object is larger than the force acting on the top of the object, causing upthrust (a resultant force upwards). Upthrust is equal to the weight of fluid displaced
• Object floats if weight = upthrust
• Atmospheric pressure is created on a surface by air molecules colliding with the surface
• Walking: 1.5 m/s

  Running: 3 m/s

  Cycling: 6 m/s

  Car: 25 m/s

  Train: 30 m/s

  Plane: 250 m/s
• Driving force must balance frictional forces to travel at a steady speed. Friction occurs between two surfaces in contact or when an object travels through a fluid
• When a object falls gravity is much greater than friction, so it accelerates, which means drag increases with speed, reducing the acceleration to the point that it is equal to friction, so the resultant force is zero
• Terminal velocity depends on shape and area. Air resistance causes things to fall at different speeds and the terminal velocity of any object is determined by its drag in comparison to its weight
• Newton's first law: resultant force is needed to make something start moving, speed up or slow down
• Investigate how Mass and Force Affect Acceleration:

  1. connect the trolley to a piece of string that goes over a pulley and is connected on the other side to a hook with a known mass
  2. the weight of the hook and any masses attached to it will provide the accelerating force, equal to the mass of the hook * acceleration
  3. mark starting line on the table place trolley on starting line, make string taut and release, record acceleration measured by light gate, which is acceleration of the whole system. repeat 2x
• Stop= Think + Break

  Thinking Distance: how far car travels during the driver's reaction time
• When the brake pedal is pushed this causes brake pads to be pressed onto the wheels, causing friction and then work to be done transferring kinetic energy to thermal store, so breaks heat up. A faster vehicle needs more work and a greater breaking force and a larger deceleration, which may the brakes to overheat and the vehicle to skid
• You can calculate how long the ruler falls for because acceleration due to gravity is constant