2.2 
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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
Section 2 review
Forces are the actions on bodies that can change their motion. Newton's three laws describe motion of objects in the presence or absence of forces. In the absence of a net force, the first law states that an object at rest or in motion will continue to be in the identical state of rest or motion. The second law states the relationship between net force, mass, and acceleration experienced by an object. The third law states that for every action force there is an equal but opposite reaction force. Torque is the result of forces that act in a rotational or twisting manner. If there is no net force or net torque on an object, then it is in static equilibrium.
Vocabulary words force, newton (N), pound, weight, free-body diagram, normal force, net force, spring constant, spring, torque, line of action, equilibrium, fulcrum, lever, friction, Newton's first law of motion, Newton's second law of motion, Newton's third law of motion, momentum, impulse

Key equations
F w =mg
F=−kx
τ=r×F
a= F m

Review problems and questions
  1. The acceleration due to gravity at the surface of Mars is 62% lower than that at the Earth. If the Mars Rover has a mass of 950 kg on the Earth, how much does it weigh on Mars? (on the Earth, g = 9.8 m/s2) Show
  1. A 100 kg astronaut weighs 500 N on a different planet. What is the acceleration due to gravity on that planet? Show
  1. A 10 kg mass is attached to a spring that is held vertically. If the spring constant is 750 N/m, how many cm does the spring stretch from its un-stretched position? Show
  1. A hockey puck that has a mass of 170 g travels with a speed of 30 m/s.
    1. What is the momentum of the puck?
    2. If the puck going at this speed hits a standing player that has a mass of 100 kg and stops, how fast would the player move backwards? (Assume that there is no friction between the ice and the skate blades)
    3. Discuss the significance of the result you have obtained in part b. Show
Mass suspended by two parallel springs
  1. A mass m = 5 kg is hung from two springs as shown on the image on the right. The springs are identical and have a spring constant of k = 200 N/m. Calculate the distance by which the springs would stretch. Show
Mass suspended by two springs connected end-to-end
  1. Two springs are now connected end to end and a mass m = 12 kg is attached as shown on the image on the right.The top spring has a spring constant k1 = 300 N/m and the bottom spring has a spring constant k2 = 200 N/m.
    1. Before you do any calculations, which spring do you think will stretch more? Explain your answer with a couple of sentences.
    2. Calculate the distance by which each spring will stretch and the total stretch distance of both springs. Show

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