When you make the Particle Model Assumption 2.5.3 (that is, no rotational motion), all kinetic energy is translational, and it is often simply called kinetic energy and written
\begin{equation*}
K = 1/2mv^2
\end{equation*}
Kinetic energy is the energy of motion. Most kinetic energy you will work with is translational. Objects that are rotating (which you will study later) have rotational kinetic energy, possibly in addition to translational kinetic energy.
ExercisesKinetic Energy Activities
1.Summarize What You Learned - Kinetic Energy.
Write a 1-2 sentence description of what the definition of kinetic energy says in words and why it makes sense given your everyday experience.
2.Sensemaking: Units.
Energy is measured in Joules (J). Use the definition of kinetic energy to write a Joule in terms of other units you are familiar with.
3.Extension: Systems with Multiple Objects.
Many systems include more than one object. In general, the different objects could have different masses and different speeds. How do you think you could find the kinetic energy for such a system? Write an equation for the total kinetic energy.
I estimated around 576,000 J. (Many cars have a mass that is somewhere around 1200 kg, and a typical highway speed limit is 70 mph, which is about 31 m/s.)
5.Explanation: Numbers for Two Cars.
Estimate the kinetic energy (in J) of a system consisting of two identical cars traveling toward each other, both traveling at the same speed. Is your answer greather than, less than, or equal to the kinetic energy for a single car you found in the previous activity? Explain why this makes sense.
