Our ancestors noticed that when amber was rubbed against fur it attracted small objects...why is this? Created by Brit Cruise.

Students demonstrate the erythrocyte sedimentation rate test (ESR test) using a blood model composed of tomato juice, petroleum jelly and olive oil. They simulate different disease conditions, including rheumatoid arthritis, anemia, leukocytosis and sickle-cell anemia, by making appropriate variations in the particle as well as in the fluid matrix. Students measure the ESR for each sample blood model, correlate the ESR values with disease conditions and confirm that diseases alter blood composition and properties. During the activity, students learn that when non-coagulated blood is let to stand in a tube, the red blood cells separate and fall to the bottom of the tube, resulting in a sediment and a clear liquid called serum. The height in millimeters of the clear liquid on top of the sediment in a time period of one hour is taken as the sedimentation rate. If a disease is present, this ESR value deviates from the normal, disease-free value. Different diseases cause different ESR values because blood composition and properties, such as density and viscosity, are altered differently by different diseases. Thus, the ESR test serves as a real-world diagnostic screening test to identify indications of the presence of any diseases in people.

The index of refraction in a material isn't always the same for every wavelength. This is how prisms split white light into so many colors. Created by David SantoPietro.

Using a one-dimensional number line to visualize and calculate distance and displacement. Created by Sal Khan.

An introduction to the difference between distance traveled and displacement. Created by Sal Khan.

Relating angular displacement to distance traveled (or arc length) for a ball traveling in a circle. Derivation of formula for arc length.

Using the same method for measuring friction that was used in the previous lesson (Discovering Friction), students design and conduct experiments to determine if the amount of area over which an object contacts a surface it is moving across affects the amount of friction encountered.

Student groups are provided with a generic car base on which to design a device/enclosure to protect an egg on or in the car as it rolls down a ramp at increasing slopes. During this in-depth physics/science/technology activity, student teams design, build and test their creations to meet the design challenge, and are expected to perform basic mathematical calculations using collected data, including a summative cost to benefit ratio.

Learn about the Doppler effect and how it explains the change in frequency of a wave when its source and an observer are moving. Created by Sal Khan.

Understanding the differences between the dot and cross products. Created by Sal Khan.

The Drawing Board consists of a marking pen that remains stationary and a platform that swings beneath the pen, acting as a pendulum. As the platform swings, the pen marks a sheet of paper that is fastened to the platform, generating beautiful repetitive patterns. These colorful designs contain hidden lessons in physics. This resource includes instructions for making a large-scale Drawing Board as well.

Students use a compass and a permanent magnet to trace the magnetic field lines produced by the magnet. By positioning the compass in enough spots around the magnet, the overall magnet field will be evident from the collection of arrows representing the direction of the compass needle. In activities 3 and 4 of this unit, students will use this information to design a way to solve the grand challenge of separating metal for a recycling company.

To gain an understanding of mixtures and the concept of separation of mixtures, students use strong magnets to find the element of iron in iron-fortified breakfast cereal flakes. Through this activity, they see how the iron component of this heterogeneous mixture (cereal) retains its properties and can thus be separated by physical means.

In this activity related to magnetism and electricity, learners discover that a magnet falls more slowly through a metallic tube than it does through a nonmetallic tube. Use this activity to illustrate how eddy currents in an electrical conductor create a magnetic field that exerts an opposing force on the falling magnet, which makes it fall at a slower rate. This activity guide also includes demonstration instructions involving two thick, flat pieces of aluminum to illustrate the same principle.

Students use a watt meter to measure energy input into a hot plate or hot pot used to heat water. The theoretical amount of energy required to raise the water by the measure temperature change is calculated and compared to the electrical energy input to calculate efficiency.

David explains what it means for a collision to be elastic or inelastic. Created by David SantoPietro.

In this activity about electricity, learners explore how static electricity can make electric "fleas" jump up and down. Learners use a piece of wool cloth or fur to charge a sheet of acrylic plastic. Then, they observe as tiny bits of Styrofoam, spices, ceiling glitter, or rice (aka "fleas") jump up to the plastic and then back down.

In this video David explains why physicists came up with the idea of the electric field, how it's useful, and explains how the electric field is defined. Created by David SantoPietro.

The direction of an electrical field at a point is the same as the direction of the electrical force acting on a positive test charge at that point. For example if you place a positive test charge in an electric field and the charge moves to the right you know the direction of the electric field in that region points to the right. Created by David SantoPietro.

Sal shows that there will be a net torque on a loop of current in a wire. Sal shows that this net torque will cause the loop to rotate. Created by Sal Khan.