CONCEPT: Motion of objects is affected by friction.
CONTENT OBJECTIVE: 5A2.00 To understand the relationship of friction to the functioning of machines
INSTRUCTIONAL OBJECTIVES: The learner will:
2.01 experimentally determine the relationship of friction to
the functioning of machines.
2.02 demonstrate that rollers can decrease frictional force and
increase speed.
2.03 research to discover other ways that friction can be reduced.
2.04 explain that friction produces heat.
OUTLINE OF CONTENT:
I. Friction produces heat and slows work
II. Importance of friction
III. Ways to reduce friction
TN COMPONENT OF SCIENCE: Habits of Mind
TN GOAL:
To enable students to demonstrate ways of thinking and
acting inherent on the practice of science; and to exhibit an
awareness of the historical and cultural contributions to the
enterprise of science.
TN THEME:
3.6 CREATIVE ENTERPRISE - Creativity contributes to
the process of science through ideas and inventions.
TN STANDARD(S): The learner will understand that:
3.6c Creativity enables development of new concepts, processes,
and attitudes toward scientific inquiry.
BENCHMARK: People use past experiences as a guide when approaching
new and unique situations.
BENCHMARK: The integration of prior knowledge with new information
may produce innovative results.
3.6d The human ability to shape the future comes from a capacity
for generating knowledge, developing new technologies and for
communicating ideas.
BENCHMARK: Humans throughout history have been toolmakers.
BENCHMARK: Although modern tools tend to be more complex than those
of the past, many are actually modifications of ancient tools.
CLASSROOM CONNECTORS
TIME REQUIRED:
Two instructional periods
MATERIALS:
Heavy books, large marbles, sandpaper, ax paper, shoe
boxes, rock, pencils, spring balance, 30 cm circle of cardboard, balloon, paper clips, rulers, 10 tin cans
SET:
(Have each student rub his/her hands together.) What is happening
to your hands? (response) The movement of force causes heat. This
is friction. Today, we are going to talk about the relationship
of friction and the functioning of machines.
INSTRUCTION:
(Define the word FRICTION to the class.) Friction
is a force produced by rubbing, that resists motion. (Have a child
push a box of books across the floor.)
(Use the illustration of the child pushing the box of books to
introduce the lesson.) Three things that must be understood about
the illustration are:
1. One must push with a lot of force to move the full box.
2. One must also overcome the inertia of the box.
3. One must overcome the force of friction created by the box rubbing against the floor.
(Explain how the box slides over the floor and how it resists the sliding movement.) The larger the mass of the box, the greater its friction. The kind of surface also affects the force of friction. Sliding friction can be reduced by making surfaces slippery. Example: skiers often put oil or wax on the bottom of the skis. Why? (response) Objects that roll have less friction than objects that slide.
Push a book across a desk top. Then put some large marbles under the book and push it again. Which is easier - sliding or rolling the book? (pause, then seek responses) Wheels are a common way to reduce friction. Pulling a wagon over a concrete sidewalk is easier than pulling a slide over it. Pall bearings are rolling objects used to reduce friction. They help axles turn with ease. Axles are used in the wheels of many machines. For example, a bicycle has ball bearings in the wheels. The axle rolls around the balls. The balls keep the axle from sliding and makes it easier to turn the bicycle's wheel. Objects can be shaped so that they have less resistance as they move through fluids. There is friction between bicycle tires and the road. Friction keeps your bicycle from skidding when you turn a corner. It is the reason that your bike, sooner or later, comes to a stop.
ACTIVE PARTICIPATION:
(To demonstrate how surfaces effect friction, get two shoe boxes. Tape sandpaper to the bottom of one and wax paper to the bottom of the other. Fill the boxes with rocks until they both weigh the same. With a spring balance, measure the amount of force needed to pull each one across a board. Set one box on a pencil. Then measure the force needed to pull it across the board. A simple spring balance can be made by fastening a strong rubber band to the end of a ruler. Hook a paper clip to the other end of the rubber band. To measure force, measure how many inches the rubber band stretches.)
(How to build a friction-reducing machine:
1. Cut a circle out of corrugated cardboard, about 30 cm. (12 in.) in diameter. Tape an empty wooden thread spool to the center of the cardboard. In the cardboard, punch a hole through to the hole in the spool.
2. Inflate a balloon and tie it with a string leaving as much of the mouth available as possible. Now put the mouth of the balloon over the end of the spool not attached to the cardboard.
3. Place the cardboard on the floor, with the balloon on top. Cut the string so that the air can escape from the balloon. Watch your machine float across the floor. This is the way friction is reduced in a hydrofoil.)
REINFORCEMENT:
(Students can do this activity to learn how ball bearings work. You will need two #10 tin cans and six equal-size marbles.)
1. With the can bottoms facing each other, place one can on top of the other. Try turning the top can around.
2. Place the marbles on top of one can and along the outside edge. Then, place the other can on top of the marbles. Now, try turning the can around. Was it easier to move the top can when the marbles were between the two cans? (response) Now, find out how ball bearings are used in machines such as bicycles and automobiles.
CLOSURE:
(Have the students write down their own definitions of friction and give one example.)
Give each student group a problem scenario in which friction is creating the problem. Each group is to come up with a solution that is economical as well as feasible and presents it to the class. Then students will write a journal entry in which they hypothesis how early man imagined the need for simple machines. (Example wheel)
INDEPENDENT PRACTICE:
(Have the students cut out or draw pictures of situations in which friction was useful and those in which it was not useful. When friction was not useful, have the students indicate how friction was reduced. When friction was useful, have the students indicate how it was increased.)
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