Measuring Kinetic Energy

Measuring Kinetic Energy

How much kinetic energy do moving objects have?

Vocabulary

Proportional relationship: the relationship between two variables when the ratio
between the variables is constant; a graph of a proportional relationship is a straight
line through the origin

Linear relationship: a relationship between two variables when a graph of one variable
versus the other is a straight line; it can be represented by the equation y=mx+b

Slope: the steepness of a line on a graph, calculated by dividing the change in the
y-value by the change in the x-value for any two points on a line

Nonlinear relationship: a relationship between two variables when a graph of one
variable versus the other is not a straight line

Constant: describes a value that does not change

1. Kinetic Energy and Mass

Energy is the ability to cause motion or change.

Kinetic energy is the energy an object has due to its motion.

Lake and rock example:

2 rocks (one large, one small); Both thrown off a cliff

Large rock has more mass so it makes a bigger splash = more kinetic energy

More mass = more kinetic energy (proportional relationship & linear relationship)

Proportional relationship: the relationship between two variables when the ratio between the variables is
constant; a graph of a proportional relationship is a straight line through the origin

Linear relationship: a relationship between two variables when a graph of one variable versus the other is a
straight line; it can be represented by the equation y=mx+b

Slope: the steepness of a line on a graph, calculated by dividing the change in the y-value by the change in the
x-value for any two points on a line

1. Kinetic Energy and Mass

Energy is the ability to cause motion or change.

Kinetic energy is the energy an object has due to its motion.

Lake and rock example:

2 rocks (one large, one small); Both thrown off a cliff

Large rock has more mass so it makes a bigger splash = more kinetic energy

More mass = more kinetic energy (proportional relationship & linear relationship)

Proportional relationship: the relationship between two variables when the ratio between the variables is
constant; a graph of a proportional relationship is a straight line through the origin

Linear relationship: a relationship between two variables when a graph of one variable versus the other is a
straight line; it can be represented by the equation y=mx+b

Slope: the steepness of a line on a graph, calculated by dividing the change in the y-value by the change in the
x-value for any two points on a line

Multiple Choice

What kind of relationship do mass and kinetic energy have?

• Proportional

• Proportional and nonlinear

• Linear

• Proportional and linear

2. Kinetic Energy and Speed

Cycling example:

Cycling races have a standing start so the cyclists have no kinetic energy.

Cyclists speed up throughout the race, so they gain more kinetic energy, but their mass doesnʼt
increase so how do they gain kinetic energy?

Kinetic energy of an object increases as the speed of an object increases

Nonlinear relationship: a relationship between two variables when a graph of one variable versus the
other is not a straight line

The mass of the cyclist doesnʼt change so that is the constant.

Constant: describes a value that does not change

Kinetic energy and speed are not proportional but kinetic energy is proportional to speed squared.

Multiple Choice

What kind of relationship do kinetic energy and speed have?

• Proportional

• Not proportional

Open Ended

What is kinetic energy proportional to?

3. Optimizing a Racing Bike’s Design

Defining the Problem

A bike with more mass will require more energy to get it to move

Bicyclists want bikes with low masses because they require less energy to accelerate to high speeds

Criteria: lightweight & strong frame

Testing Solutions

Build with different materials to test lightweightness

Engineers use a process involving a machine to “ride” the bike to make sure it can withstand long
distances of being ridden.

Optimizing the Design

Iterative testing with different models and using the qualities of successful models to build one super
design

Open Ended

List and explain the criteria for building a racing bike: