|Physical Science||Simple Machines/Technology 5A2.00||Habits of Mind||Creative Enterprise 3.6 cd|
CONTENT STANDARD: Physical Science
CONTENT TOPIC: Simple Machines/Technology
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:
TN COMPONENT OF SCIENCE: Habits of Mind
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.
(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:
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.
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.
(How to build a friction-reducing machine:
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.)
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.
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)
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