Physics and Our Universe: How It All Works

Take a quick trip from the subatomic to the galactic realm as an introduction to physics, the science that explains physical reality at all scales. Professor Wolfson shows how physics is the fundamental science that underlies all the natural sciences. He also describes phenomena that are still beyond its explanatory power.

Understanding physics is as much about language as it is about mathematics. Begin by looking at how ordinary terms, such as theory and uncertainty, have a precise meaning in physics. Learn how fundamental units are defined. Then get a taste of the basic algebra that is used in physics.

Motion is everywhere, at all scales. Learn the difference between distance and displacement, and between speed and velocity. Add to these the concept of acceleration, which is the rate of change of velocity, and you are ready to delve deeper into the fundamentals of motion.

Use basic concepts to analyze motion when an object is under constant acceleration due to gravity. In principle, the initial conditions in such cases allow the position of the object to be determined for any time in the future, which is the idea behind Isaac Newton's "clockwork universe."

Add the concept of vector to your physics toolbox. Vectors allow you to specify the magnitude and direction of a quantity such as velocity. The vector's direction can be along any axis, allowing analysis of motion in three dimensions. Then use vectors to solve several problems in projectile motion.

Circular motion is accelerated motion, even if the speed is constant, because the direction, and hence the velocity, is changing. Analyze cases of uniform and non-uniform circular motion. Then close with a problem challenging you to pull out of a dive in a jet plane without blacking out or crashing.

For most people, the hardest part of learning physics is to stop thinking like Aristotle, who believed that force causes motion. It doesn't. Force causes change in motion. Learn how Galileo's realization of this principle, and Newton's later formulation of his three laws of motion, launched classical physics.

Investigate Newton's second law, which relates force, mass, and acceleration. Focus on gravity, which results in a force, called weight, that's proportional to an object's mass. Then take a ride in an elevator to see how your measured weight changes due to acceleration during ascent and descent.

According to Newton's third law, "for every action there is an equal and opposite reaction."Professor Wolfson has a clearer way of expressing this much-misunderstood phrase. Also, see several demonstrations of action and reaction, and learn about frictional forces through examples such as antilock brakes.

Consider Newton's laws in cases of two and three dimensions. For example, how fast does a rollercoaster have to travel at the top of a loop to keep passengers from falling out? Is there a force pushing passengers up as the coaster reaches the top of its arc? The answer may surprise you.

See how the precise definition of work leads to the concept of energy. Then explore how some forces "give back" the work done against them. These conservative forces lead to the concept of stored potential energy, which can be converted to kinetic energy. From here, develop the important idea of conservation of energy.

A dramatic demonstration with a bowling ball pendulum shows how conservation of energy is a principle you can depend on. Next, solve problems in complicated motion using conservation of energy as a shortcut. Close by drawing the distinction between energy and power, which are often confused.

Newton realized that the same force that makes an apple fall to the ground also keeps the moon in its orbit around Earth. Explore this force, called gravity, by focusing on circular orbits. End by analyzing why an orbiting spacecraft has to decrease its kinetic energy in order to speed up.

How do you analyze a complex system in motion? One special point in the system, called the center of mass, reduces the problem to its simplest form. Also learn how a system's momentum is unchanged unless external forces act on it. Then apply the conservation of momentum principle to analyze inelastic and elastic collisions.

Turn your attention to rotational motion. Rotational analogs of acceleration, force, and mass obey a law related to Newton's second law. This leads to the concept of angular momentum and the all-important -conservation of angular momentum, which explains some surprising and seemingly counterintuitive phenomena involving rotating objects.

What's the safest angle to lean a ladder against a wall to keep the ladder from slipping and falling? This is a problem in static equilibrium, which is the state in which no net force or torque (rotational force) is acting. Explore this condition and develop tools for determining whether equilibrium is stable or unstable.

Start a new section in which you apply Newtonian mechanics to more complex motions. Study oscillations, a universal phenomenon in systems displaced from equilibrium. A special case is simple harmonic motion, exhibited by springs, pendulums, and even molecules.

Investigate waves, which transport energy but not matter. When two waves coexist at the same point, they interfere, resulting in useful and surprising applications. Also examine the Doppler effect, and see what happens when an object moves through a medium faster than the wave speed in that medium.

Fluid is matter in a liquid or gaseous state. Study the characteristics of fluids at rest. Learn why water pressure increases with depth, and air pressure decreases with height. Greater pressure with depth causes buoyancy, which applies to balloons as well as boats and icebergs.

Explore fluids in motion. Energy conservation requires low pressure where fluid velocity is high, and vice versa. This relation between pressure and velocity results in many practical and sometimes counterintuitive phenomena, collectively called the Bernoulli effect - explaining why baseballs curve and how airplane speedometers work.

Beginning a new section, learn that heat is a flow of energy driven by a temperature difference. Temperature can be measured with various techniques but is most usefully quantified on the Kelvin scale. Investigate heat capacity and specific heat, and solve problems in heating a house and cooling a nuclear reactor.

Analyze heat flow, which involves three important heat-transfer mechanisms: conduction, which results from direct molecular contact; convection, involving the bulk motion of a fluid; and radiation, which transfers energy by electromagnetic waves. Study examples of heat flow in buildings and in the sun's interior.

Heat flow into a substance usually raises its temperature. But it can have other effects, including thermal expansion and changes between solid, liquid, and gaseous forms - collectively called phase changes. Investigate these phenomena, starting with an experiment in which Professor Wolfson pours liquid nitrogen onto a balloon filled with air.

Delve into the deep link between thermodynamics, which looks at heat on the macroscopic scale, and statistical mechanics, which views it on the molecular level. Your starting point is the ideal gas law, which approximates the behavior of many gases, showing how temperature, pressure, and volume are connected by a simple formula.