A ball popper on a cart is shown moving on a track in 4 different animations (position is given in meters and time is given in seconds). In each animation, the ball is ejected straight up by the popper mechanism at t=1 seconds. Consider the reference frames that move along with the carts, in other words, a reference frame in which the velocity of the cart is stationary. Which of these is not an inertial reference frame?  

A ball is shown on a rotating Merry-Go-Round with a frictionless surface (position is given in meters and time is given in seconds). The ball starts at the center of the Merry-Go-Round and moves outward at a constant speed. Views from two reference frames are shown, one where the motion of the ball is shown as seen from an observer on the ground, Frame 1, and the other where the motion of the ball is shown as seen from an observer on the Merry-Go-Round, Frame 2.Which is the inertial reference frame?

The above simulations present a classic physics thought experiment, sometimes called a Gedanken experiment from the German. An object is moving to the right in a straight line with constant speed (position is given in meters and time is given in seconds. The spaceship is accelerating upward. The animation Reference Frame 1 shows what a stationary observer would see. The animation Reference Frame 2 shows what an observer in the spaceship would see. How do you write the laws of the physics so that both frames are correct? 

A boxcar travels by you at relativistic speed as shown in the animation (position is given in meters and time is given in seconds). Inside the boxcar is a woman with a laser that she turns on as she passes you. The laser light travels through the back of the boxcar. What is the velocity of the laser light that the woman in the boxcar measures, v_w, compared to the velocity of the laser light that you measure trackside, v_T? Start.

Three men, A, B, and C,  are traveling on a train that travels by you at relativistic speed as shown in the animation (position is given in meters and time is given in seconds). As B passes you, both you and B notice light signals from A and C arriving at the same time. Who emitted the signal first? Start.

A boxcar travels by you at relativistic speed as shown in the animation (position is given in meters and time is given in seconds). Inside the boxcar is a woman with a laser that she turns on as she passes you. The laser light hits the back of the boxcar. Which frame of reference  is a measurement of the time of flight for the laser laser light a proper time? Start.

A spaceship flies close to a space beacon at 70% of the speed of light (position is given in meters and time is given in seconds). The beacon emits light flashes as shown in the animation.   What is the time difference between these light flashes as seen by an observer inside the space ship? The time shown in the upper left hand corner is the time as measured in the reference frame of the beacon.  Start

An pole vaulter carries her pole towards a red barn as shown in the animation (position is given in meters and time is given in seconds). The pole is 20 m long at rest as is the barn. The vaulter carries the pole at a speed such that it is contracted as shown from the reference frame of the barn. With what velocity must the vaulter have?  Start

A triangle is shown traveling to the right as shown in the animation (position is given in meters and time is given in seconds). With what speed must the triangle travel in order to be an isosceles triangle? Start.

Two measuring sticks pass close by each other with relative speeds comparable to the speed of light (position is given in meters and time is given in seconds). A light flash occurs when the right ends of the sticks coincide, event 1, and again when the left ends coincide, event 2. Which of the following is true for all relative velocities?  You can view the events in either the green reference frame or the red reference frame.

Three men, A, B, and C,  are traveling on a train that travels by you at relativistic speed as shown in the animation (position is given in meters and time is given in seconds). As B passes you, both you and B notice light signals from A and C arriving at the same time. From your point of view, how long before C does A have to turn on his light ? Start.

Four graphs are shown representing the relativistic behavior of an electron. The slider controls the velocity of the electron (velocity is given in m/s and momentum is given in MeV/c. One graph correctly shows the momentum of an electron, which one is it?

Four graphs are shown representing the relativistic behavior of an electron. The slider controls the velocity of the electron (velocity is given in m/s and energy is given in MeV. One graph correctly shows the total energy  of an electron, which one is it?

Four graphs are shown representing the relativistic behavior of an electron. The slider controls the velocity of the electron (velocity is given in m/s and energy is given in MeV. One graph correctly shows the kinetic energy  of an electron, which one is it?

The animations above represent a cross section of a three dimensional sound or light wave propagating away from a moving source.  The animations are paired so the velocity of the source relative to the wave it produces are identical. In all of the animations the source is traveling slower than the speed of the wave it emits. Which set of Animations, A or B, represent light? Note: Only one animation will run at a time. For best results, let an A animation run until the position counter gets to about 10, then click the link to the B animation below, and pause it when its position counter gets to 10.