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
As you learned in the investigation on orbits, the Earth (and everything on it!) circles the Sun at a speed of roughly 30,000 m/s (67,000 mph). But you need to reach an even higher speed in order to fight the Sun's gravity and work your way out toward the Red Planet. The Spirit rover got the needed boost from the launch rocket, from booster rockets that fired shortly after launch, and from much smaller engines on the spacecraft itself.
Humans exploring Mars: it’s been a dream of writers and scientists for many years. The dream drew inspiration from colorful reports that astronomers had seen irrigation canals or seasonal vegetation on Mars. Today, of course, we know the planet is colder, dryer, and windier than the harshest desert on Earth: no farmers, canals, or crops are anywhere to be seen. But is Mars entirely lifeless? Could it support a human outpost? To find out, many believe, we must set foot on its dusty soil. And that can’t happen until we know what it takes to bring people to Mars—along with many tons of supplies and shelter.
Fortunately, in the past half-century we've learned a lot about reaching Mars and working there. How? With the help of unmanned spacecraft. The first such spacecraft simply cruised past the Red Planet, snapping pictures along the way. The next generation entered into orbit around Mars, ultimately mapping its entire surface. A third generation reached the planet's surface, telling us about its environment and showing us its rocky plains. Now a fourth generation of mechanical Martians is roving about the Red Planet, exploring craters and searching for signs of past or present life.
As you learned in the 
