2.1 
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Interactive Simulations   Position and displacement in one dimension    Displacement and position in two dimensions    Solve v=dx/dt for dt    Velocity, position, and time (basic version)    Velocity, position, and time (more advanced version)    Acceleration (basic version)    Acceleration (more advanced version)    Static equilibrium    Static equilibrium and the lever    Newton's second law (basic version)    Newton's second law (more advanced version)    Circular motion interactive simulation    Orbits of the planets and dwarf planets    Orbits simulation Interactive Calculators   Speed calculator    Velocity calculator    Acceleration calculator    Velocity in accelerated motion    Average velocity calculator    Hooke's law calculator    Torque calculator    Rotational equilibrium and torque    Newton's second law calculator    Momentum calculator    Angular velocity    Linear velocity and angular velocity    Centripetal acceleration    Centripetal force    Law of universal gravitation calculator
1 - Science of Physics
2 - Forces and Motion      Chapter 2 at a glance      2.1 - Motion      2.2 - Force, momentum, and Newton's laws      2.3 - Circular motion      2.4 - Solving harder physics problems      2.5 - Chapter review3 - Energy Transformations4 - Waves and Sound
5 - Electricity and Magnetism
6 - Light and Optics
7 - The Atom
8 - Linear Motion
9 - Vectors and Forces
10 - Forces
11 - Newton's Laws and Gravitation
12 - Circular Motion and Gravitation
13 - Torque and Static Equilibrium
14 - Momentum and Collisions
15 - Angular momentum
16 - Power and Machines
17 - Harmonic Motion
18 - Waves
19 - Sound
20 - Electricity
21 - Electric and Magnetic Fields
22 - Electromagnetism and Induction
23 - Light and Color
24 - Geometrical Optics
25 - Electromagnetic Radiation
26 - The Properties of Matter
27 - Thermodynamics and Heat Transfer
28 - The Atom
29 - The Quantum Theory
30 - TBD
31 - TBD
32 - TBD
33 - TBD
34 - TBD
35 - TBD
36 - TBD
37 - The atomic nucleus and radioactivity
38 - Nuclear reactions
39 - Relativity
40 - Particle physics and the standard model
41 - Electronics (semiconductors)
42 - Nuclear technology
43 - Lasers and photonics
44 - Metals, alloys and materials science
45 - Communications technology
46 - Buildings and structures
47 - Energy technology
48 - Biophysics
49 - Matter and Energy, Space and Time
50 - Energy Transformations
51 - Nanotechnology
52 - Website Videos
53 - ExtraStuff
55 - Modeling Motion, Friction, and Center of Mass
56 - Work and the Conservation of Energy
2.1 - Motion
Nothing in nature stays in the same place. Things are always moving. One of the earliest goals of physics was to understand motion. This section looks at how we describe quantitatively how objects change their position over time. You already have an intuitive sense of speed and position from experience with bicycles, cars, and maps. Physics will expand the intuitive understanding you already have and make it mathematically rigorous. By the end of this section you should be able to apply the concepts of position, speed, and acceleration to solve motion problems.
Distance and position
Are distance and position the same? The first step in describing how things move is to create a unique way to identify where things are, meaning their precise location in space. Space has units of length and distance is the separation between any two points in space. Saying an object is 3 meters away does not, however, tell you where the object is located, because distance does not include any information about direction or from where the distance is measured.
Origin of a one-dimensional system
What is the meaning of position?Position and displacement in one dimension Position in physics means a unique location in space with reference to an origin and a coordinate system. Position has units of length but also includes direction information (+ or −) and references a "zero" location, or origin. Consider a meter stick that defines a one-dimensional straight line with the origin at the zero mark. Every location along this line can be identified by a single number. In this diagram, positive positions are to the right of the origin and negative positions are to the left of the origin. A position of −0.50 meters is a half meter to the left of the start of the meter stick. The position of −0.5 meters is different from a distance of 0.5 meters because position implies an origin and a coordinate system. Note: the choice of which direction is positive is arbitrary and can change! Show Three-dimensional space
What is the origin? Origin of the geographical coordinate system of latitude and longitude The origin is a fixed reference point that you choose. In laboratory experiments you might choose the origin to be a particular point on the table or the top of a ramp. The key idea is that all position measurements are given relative to the same origin point, otherwise you would not know how to interpret them correctly. Global Positioning Satellite (GPS) devices use latitude and longitude to specify position on Earth’s surface. The origin for zero longitude is called the Prime Meridian which passes through the Royal Observatory in Greenwich, England.
How do we describe changes in position? Displacement and position A displacement is a change in position. Displacement can have positive and negative values, as can position. When negative is defined to be left of the origin, a negative displacement is to the left. A positive displacement is to the right. The position of an object is equal to the position it starts plus the displacement it moves.
Test your knowledge Test your knowledge: displacement and position A ball moves a displacement of −20 meters from where it is in the diagram. Which of the following is TRUE?
  1. The ball moves a total distance of −30 m.
  2. The ball moves a total distance of 30 m.
  3. The ball ends up at a position of −30 m.
  4. The ball ends up at a position of +10 m.
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