The Best from Conceptual Physics Alive!

with Paul Hewitt

DISC 1

Definition of Speed

The formula speed = distance/time is explained and examples are given.

 

Velocity

Velocity is explained as having both speed and direction.

 

Average Speed

Average speed is explained as being (how far you go)/(time covered).

 

Definition of Acceleration

Explanation of the formula for acceleration, acceleration = (change in velocity)/(change in time).  Acceleration is shown in a demonstration using a rolling cylinder.

 

Numerical Example of Acceleration

Examples of acceleration using a car going from 0 to 60 mi/h in 10 s.

 

Changing Velocity

Three ways to change velocity are discussed.

 

Free Fall:  How Fast?

As objects fall they pick up speed.  This change in velocity, acceleration is g = 10m/s².

 

V = gt

Velocity acquired = (10 m/s²)t.

 

Air Resistance & Falling Objects

All objects accelerate at the same rate when there is no air resistance.

 

Free Fall:  How Far?

Derivation of the formula d = (1/2)at2.

 

Falling Distance

Friends discover a mine shaft and determine its depth using physics.

 

Vector Representation:  How to Add & Subtract Vectors

Parallel vectors are added and subtracted.

 

Geometric Addition of Vectors

How to add vectors that are at right angles.

 

Projectile Motion

Using components of vectors, it is shown that when neglecting friction, the horizontal component of projectile motion doesn’t change.

 

Demo:  Projectile Motion

Demonstration of two objects dropped simultaneously, one straight down, the other thrown horizontally.

 

Newton’s Law of Inertia

Demonstrations of the law of inertia using a coat hanger and two balls of clay.

 

Demo:  The Old Tablecloth Trick

Classic demonstration illustrates the law of inertia.

 

Demo:  Inertia of Cylinder

Demonstration showing an object in motion tends to stay in motion.

 

Why You Don’t Have to Hold the Toilet Paper Roll

Examples of inertia - getting bananas and tearing off toilet paper.

 

Demo:  Weight-Mass Distinction

Demonstration of inertia.  The author lies down with an anvil on his chest, and then the anvil is hit with a sledgehammer.

 

Definition of Newton

1 kilogram weighs 9.8 Newtons on earth.

 

Force Causes Acceleration

Acceleration is caused by unbalanced force.

 

Newton’s 2nd Law

a = F l m = g

 

Free-Fall Acceleration Explained

F / M = f / m = g

 

Demo:  Friction

Demonstration showing the force of friction at constant velocity.

 

Falling & Air Resistance

Examples of a falling parachutist are used to show that heavier objects fall faster in air.

 

Pressure:  The Bed of Nails

Demonstration of inertia and pressure.  Paul Robinson lies sandwiched between beds of sharp nails while a cement block that rests on top of him is broken with a sledgehammer by Paul Hewitt.

 

Forces and Interaction

This explanation of action and reaction forces proves that you can’t touch without being touched.

 

Demo:  Action & Reaction on Different Masses

Demonstration shows that both people pull equally in a game of tug-of-war.

 

Action & Reaction on Rifle & Bullet

An example showing that while the forces are equal, the masses and accelerations are not equal.

 

Definition of Momentum

Explanation of the formula mv using a truck and a roller skate.

 

Changing Momentum - Follow Through

Ft - ∆mv

 

Decreasing Momentum Over a Short Time

Karate is used to demonstrate ∆mv in a short time produces a large force.

 

Demo:  Bowling Ball & Conservation of Energy

A pendulum demonstrates how energy changes from potential (PE) to kinetic (KE) back to potential (PE).

 

Conservation of Energy:  Numerical Example

A circus example shows that PE always adds up to the same value at all positions.

 

Machines:  Pulleys

An example of a piano that is lifted with a small force.

 

Rotational Speed

Demonstration shows the difference between linear speed and angular speed.

 

Demo:  Centripetal Force

Demonstration of a pail of water whirled in a vertical circle over the heads of the class without spilling.

 

Why a Ball Rolls Down a Hill

Demonstration shows the relationship between a ball’s center of gravity and its support

 

Simulated Gravity

Discussion of how space satellites could produce artificial gravity.

 

Locating the Center of Gravity

Demonstration shows that some objects have centers of gravity inside themselves while other objects have centers of gravity outside themselves.

 

Toppling

Examples are used to explain why some things fall over while others do not.

 

Demo:  Difference Between Torque and Weight

Demonstration illustrates the difference between torque and weight.  A broom is sawed in half, and a question is posed about the weights of the two halves.

 

Demo:  Rotational Inertia Using Weighted Pipes

Demonstration shows the different rotational inertias of two equal-mass pipes.

 

Demo:  Rotational Inertia Using a Hammer

Demonstration shows that the ease of tipping a hammer depends on its orientation.

 

Demo:  Rotational Inertia with a Weighted Rod

This demonstration extends the previous demonstration (Side 2, Chapter 6), literally, using a pole and weight.

 

Demo:  Conservation of Angular Momentum Using a Rotating Platform

Go for a spin with physics - demonstration of the conservation of angular momentum.

 

Inverse-Square Law

The concept of the inverse-square law is carried over to light, radioactivity, magnetism, and electricity.  A diagram is used to conceptually show the “inverse-square law” of gravity.

 

von Jolly’s Method of Measuring the Attraction Between Two Masses

Explanation of how von Jolly determined the numerical value of the universal gravitation constant.

 

Weight & Weightlessness

Many people believe the astronauts circling the earth are floating because they are beyond the reach of the earth’s gravity. This explanation shows that this couldn’t be further from the truth.

 

Apparent Weightlessness

A discussion of when it seems like there is no gravity - when falling objects fall at the same rate.

 

Discovery of Neptune

Perturbations in the orbit of Uranus lead to the prediction of Neptune and Pluto.

 

Gravitational Field Inside a Hollow Planet

Conceptually shows that there is no gravity field in the center of hollowed-out planet.

 

The Weight of an Object Inside a Hollow Planet but Not at Its Center

Conceptually shows that there is no gravity field off-center in a hollowed-out planet.

 

Circular Orbits

Satellite motion is explained using an imaginary huge bowling alley in the sky that circles the world.

 

The Twin Trip Animation

The award-winning 1974 animated film that illustrates the twin paradox.

 

Space & Time Travel

You don’t have to be in a spaceship to experience time travel.

 

DISC 2

Evidence for Atoms

An explanation and model of Brownian motion.

 

Atoms Are Recyclable

You are made up of atoms that are from every person who has ever lived.

 

Surface Area vs. Volume

Demonstration shows that a spherical volume has the least surface area and answers the question of why stars and raindrops are round.

 

Scaling

Should you crush up ice to cool your drink faster?  This explanation answers this question and provides more examples of using surface area to your advantage.

 

Dam Keeps Water in Place, Water Keeps Dame in Place

Diagrams are used to show how water pressure can keep a dam in place.

 

Buoyancy

The buoyancy of an object is explained using vectors.

 

Demo:  Flotation

Demonstration shows why wood floats, why clay sinks, and how to make clay float.

 

Demo:  Archimedes’ Principle

Demonstration shows the buoyant force acting on a submerged object is numerically equal to the weight of fluid displaced by that object.

 

Demo:  Air Has Weight

The air in your refrigerator weighs more than a grapefruit.

 

Demo:  Air is Matter:  Pouring Air from One Glass to Another

To show that air is matter, it is poured from one glass into another.

 

Demo:  Air Has Pressure

Several demonstrations prove that air has pressure.

 

Buoyancy of Air

Buoyancy occurs in air as well as in water.

 

Demo:  Low Temperatures with Liquid Nitrogen

The temperature of liquid nitrogen shrinks the volume of a balloon and turns a flower into one that is so brittle that it “breaks” when dropped.

 

Demo:  Thermal Expansion

A tight-fitting ring that barely fits around a ball will have plenty of room when heated.

 

Demo:  How a Thermostat Works

Demonstration showing how a bimetallic strip works.

 

The Secret to Walking on Hot Coals

Because wood is a poor heat conductor, people are able to walk barefoot on red-hot coals without harm.

 

Air is a Poor Conductor

Explanation of the insulation properties of down-filled sleeping bags, Styrofoam plastic foam, and thermal underwear in terms of air’s poor heat conductivity.

 

Boiling is a Cooling Process

Liquids transforming to gases absorb energy.

 

Demo:  Pressure Cooker and Boiling & Freezing at the Same Time

When pressure is reduced on a container of water, it boils until it freezes!

 

Condensation Is a Warming Process

When water condenses on you, you feel warmer.

 

Demo:  Adiabatic Process

Two demonstrations show that the expansion of gases is a cooling process.

 

Demo:  Longitudinal vs. Transverse Waves

The difference between longitudinal and transverse waves is shown using a Slinky spring toy.

 

Demo:  Interference & Boats

Beats are demonstrated using two tuning forks with slightly different frequencies.

 

Doppler Effect

Comparing water waves with sound waves, the author explains why there is a frequency change as a source moves toward and away from an observer.

 

Demo:  Resonance

Demonstration of a tuning fork set into motion when another tuning form is struck.

 

Resonance & Bridges

Resonance explains a bridge collapse in Manchester, England, in 1831.

 

Tacoma Bridge Collapse

This historic footage shows the vibration and subsequent collapse of the Tacoma Narrows Bridge.

 

Light & Transparent Materials

Explanation of why light slows down in glass and speeds up when it leaves.

 

Polarized Light & 3-D Viewing

Explanation of how polarized sunglasses cancel out the horizontal glare and how 3-D glasses work.

 

Demo:  Colored Shadows

Using only red, green, and blue lamps, yellow and cyan shadows are produced.

 

Demo:  Why Water is Greenish Blue

Red light subtracted from white light produces blue-green light (cyan).

 

Yellow-Green Peak of Sunlight

A discussion of the sun’s yellow-green peak in radiation.

 

Demo:  Why the Sky is Blue & Why the Sunset is Red

Demonstration shows light scattering in the atmosphere.

 

Image Formation in a Mirror

An explanation using a ray diagram shows image formation and that the distance from the mirror to the image equals the distance from the mirror to the object.

 

Demo:  Model of Refraction

Wheels on an axle rolling down an incline plane model the bending of light.

 

Refraction of Sound

The difference in speeds from different temperatures causes a bending of sound in warm air over a cool lake.

 

Soap Bubble Interference

An exhibit at the Exploratorium shows a thin, soapy film producing beautiful colors by interference.

 

The Rainbow

Explanation for the shape of a rainbow.

 

Demo:  van de Graaff Generator

Demonstration shows what happens to pie pans that are charged as they rest on the top of a van de Graaff generator.

 

Demo:  Electric Potential

Current is proportional to voltage difference.

 

Caution on Handling Electrical Wires

Explanation of how electricity contracts muscles and causes a tightening grip around a “hot” wire.

 

Birds & High Voltage Wires

Explanation of why birds don’t get electrocuted when they sit on high voltage wires.

 

Ohm’s Law

I = (voltage difference) / (resistance)

 

Alternating Current

AC current is explained using a model of an imaginary washing machine.

 

Demo:  Electric Circuits

Series and parallel circuits are shown using a car battery, wire, and light bulbs.

 

Demo:  Oersted’s Discovery

Demonstration shows the connection between electricity and magnetism.

 

Demo:  Magnetic Forces on Current-Carrying Wires

Demonstration shows the forces acting on current-carrying wires in a magnetic field.

 

Demo:  Faraday’s Law

A movement of wire in a magnetic field produces current which is proportional to the number of loops of wire used.

 

Application of E&M Induction

Explanation of how “smart lights” on highway ramp entrances detect if a car is present.

 

Electron Waves

Explanation of why electrons are at particular levels around a nucleus.

 

Radioactive Decay

Explanation of the characteristics of alpha, beta, and gamma emissions in radioactive decay.

 

Half-Life

Half-life is explained and examples are given of how this procedure is used in dating the earth.

 

Carbon Dating

Discussion of scientists using carbon dating.

 

Nuclear Fission

A recount of the history of the equation U-235 + 1 neutron produces Kr-91 + Ba-142 + 3 neutrons + energy.  (This equation predicts a chain reaction.)

 

Plutonium

Explanation of how U-239 produces neptunium which produces plutonium, and a discussion of why we didn’t have any appreciable amounts of plutonium in the environment before the 1950s.

 

Mass-Energy Equivalence

Using graphs, E = mc², and imagination, the author explains (mass/nucleon) vs. atomic number and that all nucleons don’t have the same mass.

 

Nuclear Fusion

A discussion of the sun and nuclear fusion.

 

Controlling Nuclear Fusion

A speculative discussion about unlimited energy and our reactions to a changing world.