Physics Review Flashcards
Significant Digits
- Digits 1 to 9 are always significant digits
- Leading 0’s are not significant, trailing zeros are always significant
- When adding or subtracting numbers, the number of digits behind the decimal in the answer should be equal to the least number of digits behind the decimal in the question
- When multiplying or diving numbers, the number of significant digits in the answer should be equal to the least number of significant digits in the least number
Scalar Quantities
Have magnitude only and do not include direction
- Distance, speed, time, work, mass
Vector Quantities
Have both magnitude and direction
- Displacement, velocity, acceleration, force
Distance
Scalar quantity that describes the length of a path between two points. SI unit is meters (m)
Displacement
Vector quantity that describes the straight-line distance from one point to another, as well as direction. SI unit is second (m)
Time
Scalar quantity that describes a specific point in time. SI unit is second (s)
Speed
Scalar quantity that describes the distance travelled by an object during a given time interval. SI unit is meters per second (m/s)
Velocity
Vector quantity that describes the displacement of an object during a given time interval. SI unit is meters per second (m/s)
Acceleration
Vector quantity that describes any change in the velocity of an object during a given time interval. Non-uniform motion because velocity is not constant.
- Although acceleration points in the same direction as the CHANGE in velocity, it’s not always in the same DIRECTION as the velocity itself
- Acceleration in the same direction of velocity = Speeds up
- Acceleration in the opposite direction of velocity = Slows down
Force
Vector quantity that describes a push or pull that must be exerted on an object in order to make the object move. SI unit is newton (N) or kilogram meter per second squared (kg * m/s^2)
Issac Newton
Described the relation between force and motion, in his 3 laws of motion
1) Law of Inertia - Every object in motion will remain in motion and every object at rest will remain at rest unless acted upon by an outside force; friction and gravity
2) F=ma - Force needed to change an objects motion is proportional to its mass and its acceleration
3) Reactions - For every action there is an equal and opposite reaction
Force of gravity
The force of gravity acting on an object. SI unit is Newton (N) or kilogram meter per second squared (kg*m/s^2)
- Force of gravity on earth = 9.81 m/s^2
Work
Scalar quantity that describes the energy transfered to or from an object when a force is applied to move the object. Work is done when an object moves in the direction of the force that is being applied. SI unit is Joule or kilogram meter squared per second squared (kg * m^2/s^2)
Graphical determination of work
Total work done by the force can be determined from the area under the curve of a force vs. distance graph
Kinetic energy
The energy of motion
Bulk Kinetic Energy
Energy due to the motion of a whole object
- Larger the mass or faster the object, the more bulk kinetic energy it has
Electric Energy
Energy carried by moving electric charges
- Eg. Lightning as a result of moving electrical charges
Thermal Energy
Energy due to the random motion of the molecules that make up an object
Sound Energy
Energy carried from molecule to molecule by longitudinal waves
Radiant Energy
Energy that travels as electromagnetic waves
- Eg. Sun is our largest source of radiant energy
Potential Energy
The energy that can be stored in an object for a long period of time. This stored energy can be transformed into a form of energy that can do work
Gravitational Energy
Energy as a result of an object’s distance above the Earth
Elastic Energy
Energy stored in an object when it is forced out of its normal shape
Chemical Energy
Energy stored in molecules (bonds between atoms)
- This energy is released when a chemical reaction occurs and bonds are broken
Nuclear Energy
Energy stored in the nucleus of an atom
- Released during nuclear fission, when a large nucleus breaks apart
- Released during nuclear fission, when small nuclei join together
First Law of Thermodynamics
Energy is conserved in a closed system. This means that energy cannot be created or destroyed, only transformed from one form to another or from one object to another
- The total energy of the universe is constant
Free Fall Question
Em = Ep + Ek
- When height is max, Ep = max, Ek = 0, Em = Ep
- When height is 0, Ep = 0, Ek = max, Em = Ek
- There is a middle point where Em = Ep + Ek
Em before = Em after
Ep + Ek = Ep + Ek
mgh + 0 = 0 + mv^2/2
gh = v^2/2
(masses cancel out in freefall questions)
Four Elements Theory
- All matter consists of a combination of four elements: earth, air, fire, water
- When objects burn, the fire inside of them is released
Phlogiston Theory
- Substances that could burn contained an invisible fluid called phlogiston, that flowed out of an object when it burned
- Problem: Theory implies that the mass should decrease when an object burns, but magnesium gains mass when it burns
Caloric Theory
- Caloric is a mass-less fluid found in all substances, that flows from one substance to another to another. The flow is always from warmer to cooler objects
- Problem: When holes are bored into metal to make a cannon, the metals were not hot to start with but became hot afterwards
Rumford’s Hypothesis
- When holes are bored into metal to make a cannon, the mechanical energy is converted into heat, therefore Heat = Energy
- Problem: Caloric theory was so popular that Rumford was ignored
Mayer’s Hypothesis
- Recognized that the body uses oxygen to break down food for energy, and that this same process provides heat. Discovered that bodies in colder climates use more oxygen and generate more heat than bodies in warmer climates. Further support to Rumford’s idea that Heat = Energy
- Problem: Mayer was not schooled in math or physics so his ideas were overlooked because his presentation was poor
Joule’s Theory
- Proved the relationship between mechanical energy and heat, using the following experiment:
1) Force of gravity causes the weight to fall
2) Falling weight pulls on the string, which turns the drum
3) Turning of the drum stirs the water
4) The motion of the stirrer transfers energy to the water, which causes the temperature of the water to increase - Force of gravity indirectly does work on the water
Ep (weight) → Ek (weight, drum, stirrer) → Thermal Energy (water)
Kinetic Molecular Theory
- The molecules of a liquid or gas are in constant random motion. Kinetic energy is the energy of motion. The molecules in a solid vibrate
- As the molecules move in a straight line, they collide with each other and with the walls of the container
- Heat - The transfer of thermal energy from one object to another
- Temperature - The average kinetic energy of the individual atoms or molecules in a substance
Steam Engine
- Any machine that generates steam and converts the steam pressure into mechanical motion
Heat → H20 (l) → H2O (g) → Pressure → Mechanical Motion
Second Law of Thermodynamics
No process is 100% efficient. Some energy is always lost as thermal energy.
