# Physics Definitions Table

Physics and Physical Measurement

1. Fundamental Units – seven basic units of the SI measurement system: kilogram, second, mole, meter, ampere, Kelvin, candela.

2. Derived Units – units that are combinations of fundamental units. These combinations may or may not have a separate name. (eg. 1 kg m/s2 = 1 N)

3. Accuracy - An indication of how close a measurement is to the accepted value (a measure of correctness).

4. Precision - An indication of the agreement among a number of measurements made in the same way (a measure of exactness).

5. Random Uncertainty - An uncertainty produced by unknown and unpredictable variations in the experimental situation, such as temperature fluctuations and estimations when reading instruments. (Affects the precision of results - Can be reduced by taking repeated trials but not eliminated – shows up as error bars on a graph)

6. Systematic Error - An error associated with a particular instrument or experimental technique that causes the measured value to be off by the same amount each time. (Affects the accuracy of results - Can be eliminated by fixing source of error – shows up as non-zero y-intercept on a graph)

7. Vector – a quantity with both a magnitude and a direction

8. Scalar – a quantity with magnitude only

Mechanics

9. *Displacement (s) - distance traveled from a fixed point in a particular direction

10. *Velocity (u,v) - rate of change of displacement

11. *Speed (u,v) - rate of change of distance

12. *Acceleration (a) - rate of change of velocity

13. *Newton’s First Law of Motion – An object at rest remains at rest and an object in motion remains in motion at a constant speed in a straight line unless acted on by an unbalanced force.

14. *Newton’s Second Law of Motion – An unbalanced force will cause an object to accelerate in the direction of the net force. The acceleration of the object is proportional to the net force and inversely proportional to its mass. (Fnet = ma or Fnet = Δ p/Δ t (net force = rate of change of momentum))

15. *Newton’s Third Law of Motion - When two bodies A and B interact (push or pull), the force that A exerts on B is equal and opposite to the force that B exerts on A.

16. Translational Equilibrium - net force acting on a body is zero

17. *Linear Momentum (p) - product of mass and velocity

18. *Impulse (J) - change in momentum

19. *Law of Conservation of Linear Momentum - The total momentum of an isolated system (no external forces) remains constant.

20. *Work (W) - The product of a force on an object and the displacement of the object in the direction of the force.

21. Kinetic Energy (EK) – product of ½ times the mass of an object times the square of an object’s speed

22. Change in Gravitational Potential Energy (ΔEp) – product of an object’s mass times the gravitational field strength times the change in height

23. *Principle of Conservation of Energy – The total energy of an isolated system (no external forces) remains constant. (OR – Energy can be neither created nor destroyed but only transformed from one form to another or transferred from one object to another.)

24. *Elastic Collision – a collision in which kinetic energy is conserved

25. Inelastic Collision – a collision in which kinetic energy is not conserved

26. *Power (P) - The rate at which work is done or the rate at which energy is transferred.

27. *Efficiency (eff) - The ratio of the useful energy (or power or work) output to the total energy (or power or work) input.

Gravitation

28. *Newton’s Universal Law of Gravitation – The force of gravity between two objects is directly proportional to the product of the two masses and inversely proportional to the square of the distance between them and acts along a line joining their centers. (NOTE: The objects are point masses. If they are not point masses but are very far apart, that is, the distance...

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