11.1 Distance + Displacement

11.1 Distance + Displacement

11.1 Distance + displacement

  1. The motion of an object looks different to observers in different frame of reference.– ex) I’m watching my friend running on the street in my car. – my frame of reference is my car
  2. The SI unit for measuring distance = meter(m)
  3. The direction and length of a straight line from the starting pt to the ending pt of an object’s motion is displacement
  4. Displacement and velocity are examples of vectors b/c they have both magnitude and direction.

11.2 Speed + velocity

  1. Speed is measured in units of m/s.
  2. A car’s speedometer measures instantaneous speed.
  3. is the equation that defines average speed
  4. A constant slope on a distance-speed graph indicates constant speed.
  5. A difference between speed and velocity is that velocity indicates the direction of motion and speed does not.
  6. A distance-time graph indicates an object moves 20km in 2h. The average speed of the object is 20km ÷2h = 10km/h.
  7. Because its direction is always changing, an object moving in a circular path experiences a constant change in velocity.

11.3 Acceleration

  1. A moving object does not accelerate if its velocity remains constant. (accelerate = gets faster or slower –negative acceleration = slowing down)
  2. Freely falling objects accelerate at 9.8m/s2 b/c of force of gravity of the earth acts on them.
  3. The velocity of an object moving in a straight line changes at a constant rate when the object is experiencing constant acceleration.
  4. The acceleration of a moving object is calculated by dividing the change in velocity by the time over which the change occurs.
  1. Accelerated motion is represented by curved line on a distance-time graph.
  2. A car that increases its speed from 20km/h to 100km/h undergoes positive acceleration.
  3. Instantaneous acceleration is how fast a velocity is changing at a specific instant.

Know the graphs of constant speed and constant acceleration (my study guide 11.3)

12.1 Forces

  1. A push or pull is an ex. of an force
  2. The type of force measured by a grocery store spring scale is weight.
  3. The sum of all the forces acting on an object is called the net force
  4. If the forces acting on an object produce a net force of zero, the forces are called balanced forces.(-no net force  no change in motion)
  5. The force that opposes the motion of objects that touch as they move pass each other is called friction. (depends on weight of the object, types of surface ex), bigger weight, rough surface  greater friction)
  6. It usually takes more force to start an object sliding than it does to keep an object sliding b/c static friction is usually greater than sliding friction.
  7. The two forces acting on a falling object are gravity and air resistance.
  8. When a falling object reaches terminal velocity, the net force acting on it is zero.
  9. The drag force acting on falling sky diver is also known as air resistance.
  10. The pathof motion of a thrown javelin is an example of projectile motion.

12.2 Newton’s 1st + 2nd laws of motion

  1. The tendency of an object to resist any change in its motion is called inertia.
  2. During a head-on auto collision, inertia causes a passenger the front seat to continue moving forward.
  3. The acceleration of an object is equal to the net force acting on the object divided by the object’s mass. Force(N) = mass(kg) ×acceleration (m/s2)
  4. The force of gravity acting on an object is the object’s weight.(gravity = attractive force between 2 masses)

12.3 Newton’s 3rd Law

  1. When you push on a wall, the wall pushes back on you. (Newton’s 3rd Law – action-reaction)

14.1 Work + power

  1. For work to be done on an object, the object has to move.
  2. Any part of a force that does not act in the direction of an object’s motion does no work on an object.
  3. The SI unit of work is the joule.
  4. You calculate work by multiplying the force acting in the direction of motion by the distance of the object moves. Force(N) W = F*d (directions of force + moving distance should be parallel)

1N x 1m = 1N-m = 1J

(direction of force exerted parallel to the direction of the movement)

  1. The rate at which work is done is called power.
  2. The SI unit of power is watt (W). : watt=J/s
  3. The watt and the horsepower are both units of power.

14.2 Work + Machines– machines do same work

  1. A machine is a device that changes a force.
  2. A device that changes the size or direction of force used to do work is called machine.(usually decreases force by increasing distance)
  3. The force that is exerted on a machine is called the input(effort) force.
  4. Besides a reduction in friction, the only way to increases the amount of work output of a machine is to increase the work input.
  5. The mechanical efficiency of any machine is always less than 100% due to friction.

15.1 Energy + its forms

  1. Energy of an object increases when work is done on the object.
  2. Energy + work are measured in the SI uni called joule (J).
  3. If the mass of an object doubles, its kinetic energy doubles. KE=1/2 mv2
  4. The kinetic energy of an object is proportional to the square of its velocity.
  5. Energy that is stored due to position or shape is called potential energy.
  6. When a pole-vaulter flexes the pole, the pole-vaulter increases the pole’s elastic potential energy. (15.2)
  7. You can calculate an object’s gravitational potential energy by using the equation, PEg=mgh(mass(kg) × 9.8m/s2 × height(m)
  8. The sum of the kinetic energy and potential energy of an object is called mechanical energy.
  9. The 6 different forms of energy are nuclear, electrical, thermal, chemical, electromagnetic, and mechanical.

15.2 Energy conversion + conservation

  1. Wind turbines convert kinetic energy into electrical energy.
  2. The process of changing ene4rgy from one form to another is called energy conversion.
  3. “Energy cannot be created or destroyed” is a statement of the law of conservation of energy.
  4. When an apple falls from a tree to the ground, the apples’ beginning kinetic energy (0 b/c no velocity) and ending gravitational potential energy (0 b/c no height) is both equal to zero
  5. the kinetic energy of the pendulum bob decreases between locations 1 2

Energy of a Pendulum

16.1 Thermal energy + matter+16.2

  1. A measure of how hot or cold an object is compared to a reference pt can be measured in units of temperature or average kinetic energy of particles of the object.
  2. Heat is the transfer of thermal energy b/c a temperature difference.
  3. a hot dinner plate has higher thermal energy than a similar dinner plate at room temperature.
  4. If the temperature change of an aluminum nail is negative, thermal energy is transferred from the nail to the surroundings.
  5. The transfer of thermal energy with no transfer of matter is conduction. (radiation)
  6. The transfer of energy as waves moving through space is called radiation.
  7. The type of thermal energy transfer in fluids is convection.
  8. As an object’s temperature increases, the rate at which it radiates energy increases.

17.1 Mechanical waves – waves = traveling disturbances that carries E

  1. You can make a wave in a rope by adding energy (shake) at one end of the rope.
  2. Instead of crests and troughs, as in an ocean wave, a longitudinal wave has compressions and rarefactions.(compression=molecules of medium close each other; rarefactions = molecules of medium apart from each other)
  3. The crest of a traverse wave is most similar to a compression in a longitudinal wave. (crest=maximum displacement upward of medium particles)
  4. A wave in a rope is a traverse wave, but a sound wave is a longitudinal wave.
  5. Waves in a rope are transverse waves because the medium’s vibration is perpendicular to the direction in which the wave travels. (cf. longitudinal w = parallel to the direction of wave)
  6. A pebble drops straight down into a tub of water, setting surface waves that travel between the water and air.
  7. In a transverse wave, wavelength is measured from crest to crest or from trough to trough.
  8. To determine the speed of a wave, you must know the wave’s wavelength and frequency.

17.2 Properties of mechanical waves

  1. If a wave has a wavelength of 2m and a frequency of 3.0 hertz, its speed is 6m/s. (speed = frequency × wavelength) ; (period x frequency =1)
  2. To compare the energy of different waves, measure the amplitude of the waves.
  3. Amplitude measures the greatest displacement of a wave from the rest point/position.

17.3 Behaviors of waves(reflection, refraction, constructive/destructive interferences, standing waves)

  1. A wave entering a new medium at an angle will undergo refraction as one end of the wave changes speed.
  2. Ocean waves will not bend if they approach the shore at the right angle.
  3. If two waves collide and form a temporary larger wave, the interference is constructive. (crest/trough at same position  2 amplitudes add up.)
  4. At the nodes of a standing wave, there is no displacement from the rest position. (standing waves seem to be not moving, nodes and antinodes alternating)

17.4 Sound + hearing(sound = longitudinal waves)

  1. The standard measure used to compare sound intensities is the decibal (dB). – increase 10dB  10times louder; increase 40db  104 louder
  2. When a person plucks a guitar string, the number of half wavelengths that fit into the length of the string determines the pitch of the sound produced.
  3. On a piano, striking strings with the hammers sets up vibrations between the strings and the soundboard.
  4. The part of the ear that collects sound waves and focuses them inward is the outer ear.

Infrasound (frequency lower than S) S(sounds audible to human ears) ultrasound (frequency higher than S)

Speed of sound (V) higher in medium w/ compact particles (Vsteel>Vwater>Vair)

18 Electromagnetic spectrum + light

Light= particles (photoelectric effect: e- changes w/ metal only with blue light not with red light b/c Eblue light>Ered light

Light = waves (Thomas Young’s experiment) – refracts

Electromagnetic spectrum – all electromagnetic w arranged in order of frequency/wavelength – gamma rays (highest freq – shortest λ; radio waves (lowest freq – longest λ)

  1. Electromagnetic waves are transverse waves consisting of changing electric and magnetic fields.(18.1)
  2. Warm objects give off more infrared radiation than cool objects give off. (18.1)
  3. The speed of light ina vacuum is 3×108m/s. (18.1)
  4. The farther away you are from a light source, the less intense it is.(18.1)
  5. Objects that scatter some of the light that is transmitted through them are translucent. (18.3)
  6. When viewed in a red light, an object that reflects all the colors of light will appear white. (18.4)
  7. Electromagnetic waves can travel through a vacuum. (18.1)
  8. Light is produced when electrons change energy levels in an atom. (18.1)
  9. Visible light waves have a shorter wavelength than infrared waves have(18.2)
  10. A transparent objecttransmits almost all of the light that strikes it. (18.3)
  11. The electromagnetic waves with the shortest wavelengths are gamma rays. (18.2)

21.2 Electromagnetism

  1. A charged particle moving in a magnetic field will be deflected in a direction perpendicular to the magnetic field.
  2. When the current direction of a current-carrying wire is reversed, the wire will be deflected perpendicular to the magnetic field in the opposite direction.
  3. In a solenoid, there will be no magnetic field if there is no current in the wires of the coil.
  4. The strength of an electromagnet depends on the current in the solenoid, the number of coils, and the type of ferromagnetic materials in the core.
  5. An electric motor converts electrical energy into mechanical energy.

21.3 Electrical energy generation + transmission

  1. The statement that a voltage can be induced in a conductor by a changing magnetic field is known as Farraday’s Law.
  2. Moving a magnet through a wire coil can produce an electric current in the coil.
  3. A generator converts mechanical energy into electric energy.
  4. Large power plants in the United States currently use AC (alternating current) generators.
  5. Step-up transformers decrease the current and increase the voltage in the output circuit.
  6. Transformers only work with alternating current.
  7. The energy source used to produce most of the electrical energy in the United States is coal.