# NLN PAX Science: Physics

aim of physics

to understand the physical laws and principles that influence every aspect of daily life

displacement of an object

the distance that an object is from some starting point, and is measured in units of length

How does displacement change when an object is in motion?

it is constantly changing

How is motion described?

by displacement, velocity (speed) and acceleration

speed

distance traveled by an object per unit of time
speed = (distance traveled/time)

velocity

speed in a given direction

What two things does velocity tell us about a moving object?

its speed and direction

acceleration

the rate of change in velocity; can be any change in velocity, either positive or negative.

deceleration

negative acceleration or a decrease in velocity and can change in direction

How is acceleration calculated?

(final velocity-original velocity)/time

Why can velocity and acceleration be described using vectors?

because they have both magnitude and direction

What quality do all moving objects have?

momentum; an object traveling at a specific velocity has momentum

calculate momentum

Momentum = mass x velocity

conservation of momentum

the total movement of an isolated system is always constant, ie during a collision, the momentum of each body changes but the total momentum is conserved. One object may lose momentum, but this momentum is gained by other object

How is momentum conserved when a moving object hits a stable object, such as a bullet hitting a wall?

the moving object, like the bullet, delivers an impulse to the wall, and this impulse is said to be the change in the objects momentum

Newton's first law

objects in motion tend to stay in motion and objects at rest tend to stay at rest

inertia

the property of matter that resists any change in motion

Newton's second law

describes the relationship between force, mass and acceleration; the force of an object equals the mass of the object times its acceleration
f = ma

newton

the unit that represents a force that accelerates a mass of 1 kg 1 meter per second

friction

force that is exerted on an object along a surface or whenever an object has a velocity along a surface and the two surfaces touch

gravity

the force of attraction between all objects in the universe

what determines the weight of an object?

the pull of gravity on an object

Why is the Earth's gravitational force great?

because the Earth has a large mass

Is the force due to gravity and the acceleration of an object towards earth the same?

the force due to gravity is not the same on every object and depends upon the object's mass, and the acceleration toward earth is the same for all objects, independent of their mass

How does a change in the force of gravity change an objects weight and mass?

it changes the object's weight but not its mass

density

d=m/v

What is torque and what does it measure?

the perpendicular force times the lever arm; the ability of a force that is applied perpendicularly to rotate an object around an axis, ie using a wrench to turn a bolt

What is centripetal force?

continual force on an object pulling it towards the center of the circle

What does Newton's third law state?

that for every action there is an equal and opposite reaction

What is energy?

the ability to do work?

What are the two types of energy?

1. Kinetic energy
2. Potential energy

Describe kinetic energy?

energy associated with motion, any moving body has this energy because it is able to do work by moving other bodies; tells us how much work body can do by moving other bodies until it is brought to rest

How do you calculate kinetic energy?

kinetic energy = 0.5( mass x velocity)^2

What is potential energy?

the energy stored in a body because of its position, has more potential energy at the top of a hill than at the bottom

What is work?

the product of the force applied to an object and the distance through which the force is applied

How do you calculate work?

work = force x distance

What is a joule?

the unit of energy equal to the work done by a force of 1 newton acting over a distance of 1 meter

What is power?

the rate at which work is done

What is the formula for power?

power = (force x distance)/ time = work/time

What is a machine?

a device that makes work easier by changing the force or the direction of an applied force

What is the efficiency of a machine?

the work done divided by the energy used to power the machine

Why can't a machine ever be 100% efficient?

because of friction

What are the six simple machines?

1. inclined plane-slanted surface used to raise an object
2. wedge-moving inclined plane
3. screw-inclined plane wrapped around a cylinder
4. lever-simple machine that is free to move around a fulcrum when force is applied
5. pulley-chain or rope wrapped

What is a compound machine?

two or more simple machines

What is an atom?

smallest particles of an element that retain all chemical properties of an element

What is the kinetic theory of matter

atoms in matter are in a constant state of motion

What are the three ordinary states of matter, and in which states are molecules free to move around?

1. gas
2. liquid
3. solid
free to move around in liquid and gas states

Where does pressure come from?

it results from the impulses from the collision of molecules with the walls of the container

What does Boyle's Law state?

the volume of a fixed amount of gas varies inversely with the pressure of the gas. If volume of gas is decreased both the number of particle collisions and the pressure of the gas increase. If volume increases, pressure decreases

What does Charles' law state?

defines the relationship between the temperature and volume of of a gas. Volume of a fixed amount of gas varies directly with its temperature. If the temperature increases, the volume increases

What is temperature?

a measure of the average kinetic energy of the particles in a substance; tells how warm or cold a substance is with regards to other substances

What does temperature determine?

whether a substance gains or gives up heat when put into contact with other bodies.

What is heat?

a form of energy that causes the particles of matter to move faster and farther apart

What is the specific heat of a substance?

the heat needed to raise the temperature of 1 gram by 1 degree.

What is is a phase change?

the physical change of a substance from state to another

What is latent heat?

the heat energy needed per unit mass to change the phase of a substance

What is the ice point?

the temperature at which ice melts or water freezes F 32 C 0

What is the steam point?

the point at which water at standard pressure boils C 100 F 212

What is the triple point?

point on the Kelvin scale where water exists simultaneously as a gass, a liquid and a solid.

What is absolute zero?

the lowest possible temperature on the Kelvin scale.

What is motion?

a change in position relative to a frame of reference

What is a wave?

a rhythmic disturbance that travels through matter or space

What does wave motion accomplish?

a means of transferring energy

What are the two types of waves?

transverse waves and longitudinal

What is a transverse wave?

a wave in which matter vibrates at right angles to the direction in which the wave travels, ie waves on the ocean

What is a longitudinal wave?

a wave in which matter vibrates back and forth along the path that the waves, ie sound waves

What is periodic motion?

motion that repeats itself over and over again, such as the motion of a pendulum

What is a periodic wave?

a motion that repeats itself at regular intervals and that transfers energy but not mass

What is a period?

the time it takes for motion in a periodic wave to repeat itself and is measured in seconds

What is a cycle in periodic motion?

one complete repetition of a periodic event

What does a frequency of a wave tell us?

how often a cycle repeats itself in a specific time unit

How is frequency often measured?

in Hertz (Hz) which is equivalent to cycles per second

What is amplitude?

refers to the maximum distance a wave rises or falls as it travels, and it is related to the energy that the wave carries

What is amplitude related to in sound and light?

Brightness for light, loudness for sound

What is the crest of the transverse wave?

the maximum upward displacement

What is the trough of a transverse wave?

maximum downward displacement

What is the wavelength of a transverse wave?

the distance between two successive crests

What is the wave speed of a transverse wave?

the frequency of a wave times the wavelength

What is diffraction?

the bending of lightwaves around an obstacle

What happens when two waves meet?

they combine and form a new lightwave

What is interference of a wave?

how the two waves interact whith each other when they go through the same portion of a medium at the same time

What is resonance?

when the vibration of one system results in vibration of the other system of the same frequency

What are photons?

streams of tiny packets of energy

What determines what kind of light wave is produced?

the amount of energy in the photons

Why are light rays called electromagnetic waves?

because the moving photons generate electric and magnetic fields

What is the electromagnetic spectrum?

the complete spectrum of light, arranged in order of their wavelengths

What is visible light?

the portion of the electromagnetic spectrum that is visible to the human eye

What types of waves make up the electromagnetic spectrum?

infrared waves
visible light
ultraviolet rays
x-rays
gamma rays

What type of waves are sound waves?

longitudinal waves, vibrate in the direction of their motion

What part of the sound wave determines pitch?

frequency

What determines the loudness of a sound?

amplitude

When does the doppler effect occur?

whenever there is relative motion between the source of waves and the observer

What does reflection mean with regard to sound waves?

when a light wave bounces off a surface and does not absorb its energy

What is refraction?

the bendig of light rays as they pass from one medium to another; happens because light moves at different speeds through different mediums

What is dispersion?

the separation of light into its component colors

What is a lens?

any transparent material that refracts light

What is a convex lens?

thicker in the center than it is at the edges

What happens when parallel rays of light pass through a convex lens?

they converge or bend towards the center, creating a focal point

What is a focal point?

the point at which light rays meet after passing through the convex lens

What is a concave lens?

a lens that is thicker at the edges than it is in the middle

What hapepns to light rays when they pass through a concave lens?

they diverge because they are bent towards the edges

What is Coulomb's law?

like forces repel each other and unlike forces attract each other. The electric force between two charges is proportional to the product of two charges

What is magnetism?

a force of attraction

When do magnetic fields exist?

whenever electric charges are moving

When does torque result?

when moving charges are in a wire that loops

What is torque the basis of?

electric motors

What is a generator?

a device that converts mechanical energy, such as water coming down a water fall, into electric energy

What is electric potential energy?

the potential interaction of two objects' charges

What is potential difference?

the change in electrical potential energy

What is a transformer?

a device that changes the potential difference of electricity

What is voltage?

another term for potnetial difference, a measure of potential energy available

What is a voltmeter?

a device that measures the potential difference between two points in an electric current

What is a current?

electricity moving throughout a circuit

What is an ampere?

the unit used to measure electrical current?

What is an ammeter?

a device that measures the current going through any specific point on the circuit

What is a resistor?

the way by which the ability to flow through a circuit is limited?

What are the two different kinds of circuits?

1. series circuit
2. parallel circuit

What is a series circuit?

has all of its resistors in a row so that all current must travel through all resistors

What is a parallel circuit?

all the resistors are arranged side by side so that they are all the same voltage

How is electrical power calculated?

power = voltage x current

How is power expressed?

in watts: watt = volts x amperes

What is the mass defect?

the mass of the nucleus is heavier than all of the protons and neutrons that make it up, this difference between nucleus and p&n

the phenomena where an atom's nucleus could spontaneously disintegrate while giving off energy in the form of alpha and beta particles and gamma rays

the spontaneous change in the nucleus of an atom

What is transmutation?

the conversion of one element into another element

What is a nuclear reaction?

when a radioactive nucleus goes through a transmutation

What are the two main processes of nuclear reactions?

1. fusion
2. fission

What happens during fusion in nuclear reaction?

the nuclei of several light atoms combine to form a single heavy nuclus with a release of energy

What happens during fission in nuclear reactions?

a heavy nucleus splits into two main pieces with the release of a huge amount of energy