Students who demonstrate understanding can: Construct and interpret graphical displays of data to describe the relationships of kinetic energy to the mass of an object and to the speed of an object.
Clarification statement: Emphasis is on descriptive relationships between kinetic energy and mass separately from kinetic energy and speed. Examples could include riding a bicycle at different speeds, rolling different sizes of rocks downhill, and getting hit by a wiffle ball versus a tennis ball.
Official wording from the Next Generation Science Standards (NGSS Lead States, 2013). NGSS is a registered trademark of WestEd. Neither WestEd nor the lead states and partners that developed the NGSS were involved in the production of this page, and they do not endorse it. View on nextgenscience.org
Anything that moves has kinetic energy, the energy of motion. Two factors decide how much: the mass of the object and its speed. Students learn to collect or use data, put it on graphs, and describe the two relationships separately.
The mass relationship is straightforward. Double the mass at the same speed and the kinetic energy doubles, so the graph is a straight line through the origin. A loaded truck moving at the same speed as an empty one carries more energy, which is why it is harder to stop. The speed relationship is stronger and curved. Double the speed and the kinetic energy becomes four times as large; triple it and it is nine times as large.
That curve explains everyday observations: a bike crash at 20 miles per hour is far worse than at 10, and a fast tennis ball stings more than a slow wiffle ball. Students interpret the shape of each graph and use it to predict, without needing to memorize a formula.
Students often assume a straight-line relationship for speed. Data shows the kinetic energy becomes four times larger, because it depends on the speed squared.
A slow bowling ball can have less kinetic energy than a very fast baseball. Both mass and speed matter.
If an object is not moving relative to the frame chosen, its kinetic energy is zero, even if it has lots of stored energy.
To see each relationship, one variable must be kept constant. Graphing data where both mass and speed change hides the patterns.
A 1 kg cart has these kinetic energies: 2 m/s gives 2 J, 4 m/s gives 8 J, 6 m/s gives 18 J. Describe the relationship and predict the kinetic energy at 8 m/s.
Answer: Kinetic energy increases with the square of speed; at 8 m/s the cart has 32 J.
Roll balls of different masses down the same ramp into a paper cup and measure how far the cup slides, then roll one ball from different heights to vary speed. Students graph cup distance against mass and against speed and compare the shapes of the two graphs.
Assessment typically shows a graph or table and asks students to describe the relationship or pick the matching graph. Train students to name what is held constant in each data set before describing a pattern.
Original questions written for this standard. Choose an option or type your answer, then press Check. Every question has a worked explanation.
Answer: D) Twice as much
At constant speed, kinetic energy is proportional to mass, so twice the mass means twice the kinetic energy.
Answer: A) It becomes four times as large
Kinetic energy depends on speed squared, so doubling the speed multiplies the energy by 2 × 2 = 4.
Answer: 45 (also accepted: 45 j)
Tripling speed multiplies kinetic energy by 3 × 3 = 9, so 5 × 9 = 45 J.
Answer: C) A straight line through the origin
Kinetic energy is proportional to mass, so the graph is a straight line starting at zero.
Answer: D) Kinetic energy at double speed is four times as large
Doubling speed quadruples kinetic energy, so much more energy must be absorbed in the crash.
Answer: kinetic energy (also accepted: kinetic)
Kinetic energy is the energy of motion.
Use evidence to construct an explanation relating the speed of an object to the energy of that object.
A full lesson with slides, activities and an exit ticket on kinetic energy, mass and speed, pitched to grades 6-8 and editable in PowerPoint or Google Slides.
Make a lesson →A printable, differentiated worksheet on MS-PS3-1 with an answer key, ready in about a minute.
Make a worksheet →Turn kinetic energy, mass and speed into a quiz students answer online that marks itself, with a class summary for you.
Build a test →The emphasis is on describing the relationships from graphs and data. Some classes introduce the formula, but students mainly need to recognize the linear mass pattern and the curved speed pattern.
Each relationship can only be seen clearly when the other variable is held constant, which is also good investigation practice.