Download Action-at-a-Distance Forces Contact Forces

Hands-on Science, Grades 6-8
Dr. Michael Donaldson
Lesson 2: Energy and Motion
September 16, 2010
SCOPE AND SEQUENCE
In the previous workshop, we learned about matter, which is one of the most
fundamental concepts in physical science. An equally fundamental concept is that of
energy. Energy is defined as “the ability to do work.” And the definition of work is
force exerted over a distance (a mass must move some distance in order for work to
occur). The definition of force is something that exerts a push or pull with the ability to
change the velocity of an object. A change in velocity is called acceleration. Resistance
to change in velocity is called inertia. The greater the mass of an object, the more inertia
it has.
The table below lists various types of forces. There are several fundamental
forces, otherwise known as action-at-a-distance forces, and many other forces, called
contact forces, that are the result of some combination of action-at-a-distance forces.
Action-at-a-Distance Forces
Contact Forces
Gravitational Force
Electrical Force
Magnetic Force
Atomic (weak and strong)
Frictional Force
Tensional Force
Normal Force
Air Resistance Force
Applied Force
Spring Force
Energy may be either stored or active. Potential Energy is stored energy due to
composition, position, or condition, whereas kinetic energy = energy of motion, which
can either be the motion of heat or work. In the figure below, the skier initially has lots
of gravitational potential energy. As he slides down the hill the potential energy is
converted into kinetic energy, which reaches its maximum at the bottom of the hill, then
begins to be converted back to potential energy as the skier travels up hill.
Source: ISAM 2010
Energy may be stored in a number of different ways. In gravitational potential
energy, energy is stored in the object’s height. Chemical potential energy occurs when
energy is stored in the object’s molecules. Energy may be stored in a stressed object.
This is mechanical potential energy. Finally, energy may be stored as a separation of
charged particles; this is called electrical potential energy, or voltage.
Stored energy may be transformed into kinetic energy, and visa versa. The only
transformation that cannot happen to energy is the destruction of it. Because the law of
conservation of energy states that energy can neither be created nor destroyed. It can
merely be transformed from one form to another. And it is the transformation of energy
that makes stuff go.
For example, when a leaf captures the sun’s energy, it turns the light energy into
chemical energy (sugar). When you eat an ice cream cone, the chemical energy stored in
the sugar gets converted to heat and work energy that allows you to run (mechanical
energy). If you run in a squirrel cage connected to a generator, then you can convert
your energy into electrical energy, which could be stored in a battery. A battery could
be used to turn on a light. So, now we’re back to light energy. However, most of the
energy we started with was lost as heat.
Source: www.accessexcellence.org
Heat is a form of kinetic energy and travels either by radiation, conduction or
convection. Heat energy from the sun is an example of radiation. The energy is able to travel
through space in the absence of matter. The other two forms of heat movement involve matter.
In conduction, heat energy causes particles of matter to vibrate, which in turn causes
neighboring particles to vibrate. Convection occurs the transfer of heat occurs by the actual
movement of the warmed matter. Wind and ocean currents are largely caused by convection.
In this week’s laboratory, we will explore the interaction between force and
energy in the motion of matter.
KEY CONCEPTS:
• energy is a property of many substances; is associated with heat, light, electricity,
mechanical motion, sound, nuclei, and the nature of a chemical; and is transferred in
many ways.
• energy can neither be created nor destroyed
• a force is required to change an object’s velocity.
• Forces may be an action-at-a-distance, or contact force
VOCABULARY TERMS:
• Potential (stored) energy
• Kinetic (moving) energy
• Mechanical, chemical, electrical,
light energy
• law of conservation of energy
• Work
• Acceleration
• Inertia
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Action-at-a-distance force
Contact force
Heat
Conduction
Convection
Radiation
THOUGHT QUESTIONS:
1. What are two forms of kinetic energy?
2. What form of energy is stored in sugar molecules?
3. What is the difference between inertia related to mass?
4. What are different ways heat is transferred?
FOR FURTHER STUDY:
http://www.energy.gov/forstudentsandkids.htm
NEXT LESSON: Physical science experiments