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Simple Machines. Activity 1. Simple Machines. Force – push or pull on an object Newton – international unit of force. Simple Machines. Work is accomplished when an object moves as a result of force acting upon it Joule – unit of measurement for work Work = force X distance.

Simple Machines

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Simple Machines

Activity 1

Simple Machines

• Force – push or pull on an object

• Newton – international unit of force

Simple Machines

• Work is accomplished when an object moves as a result of force acting upon it

• Joule – unit of measurement for work

• Work = force X distance

Simple Machines

• How many joules of work will be required to move 75 books from the floor to a shelf 2 meters high, if each book requires a force of 2 Newtons to lift?

Extensions

• In Science work is only done when a force produces movement of an object.

• Write down as many specific examples as you can of the use of the word work in any context, science or otherwise, examples:

• Going to work

• Studying for a test is hard work

• Working on a car

Extensions

• Create 3 math problems based on the equation W = F x d. Calculate your answers. Exchange your problems with another person to solve.

• Karl Oskar has a toy mouse that needs 2 newtons of force to move it. He batted it 3 meters across the room. How much work did Karl Oskar accomplish?

• F x d = W

Extensions

• Weight – the force of gravity – is measured in newtons. Convert your weight from pounds to newtons by multiplying your weight in pounds by 4.448.

Machines

• Machines:

• Mechanical devices that permit people to do work more easily

• Provided by machines to perform work with less effort

Simple machines

• A simple machine requires only the force (effort) of a human or animal to perform work.

• There are six types of simple machines:

lever, wheel and axle, inclined plane,

pulley, wedge, and screw

Levers

• Levers are simple machines that transmit, and sometimes magnify force.

• All levers consist of four components:

• An arm (a beam or a bar)

• A fulcrum (a pivot point)

• A load (the object to be moved)

• An effort (the force needed to move the load)

Three classes of levers

L EFirst Class

Fcrowbar, shovel,

claw hammer

LESecond Class

F hinged door, wheelbarrow,

pry-up bottle opener

Three classes of levers

E LThird Class

F fishing rod, broom

baseball bat

Catapult Reflection

• Did your catapult fling the marshmallow farther with the modifications you made?

• Why do you think this happened?

• After listening to other groups, what type of modification seemed to work the best?

• What did you learn about how levers work from the catapult activity?

• What did you learn about how levers help humans do work?

Quiz 1

• Force:

• Newton:

• Work:

• Joule:

• Formula for Work:

• Simple machine:

• Six types of simple machines:

• Draw a first class lever, label the parts

Friction

• Friction is the resistance created by two surfaces rubbing together.

• When two objects are rubbed together, the friction between the two surfaces produces heat.

Friction

• The smoother the surfaces that rub together, the less friction there will be.

• Lubricant: a substance that reduces friction between moving parts.

Friction Extensions

• Tie one end of a length of string to a door knob or other handle. Tie the other end to a heavy object. Position the object on the floor so the thread is stretched taut. Use a paper clip as an S hook, hang it on the top of the thread slope and hang a washer on the paperclip hook. Time how many seconds it takes for the washer to reach the floor. Repeat using more washers, one at a time. Make a bar graph with your observation information. What did you discover?

Friction Extensions

• What is friction good for? Make a list, share it with your neighbor.

Wheel

• A disc that turns around an axis and transfers force to and from an axle.

• Function of a wheel is to reduce the amount of friction between the surfaces of two objects as one passes over the other

Wheel and Axle

• Transfers and magnifies force like the lever does

• An axle is a shaft inserted into the center of a wheel. For each revolution of the axle, the wheel makes one revolution and vice versa.

Wheel and Axle

• W = F x d

• If W stays constant, and d is changed, what happens to F?

• Force decreases when it is transferred from the axle to the wheel.

Gears

• Gear- special type of wheel with small evenly spaced teeth on the outside edge.

• Force is transferred from one gear to another

• Driving gear – one that moves a second gear

• Driven gear – a gear moved by the driving gear

• Gear ratio – the relationship between the rate of rotation of each gear.

Inclined Planes

• Inclined Plane does not move, objects move across it.

• If the amount of work remains the same, and distance is increased, the force (or effort) must decrease.

Inclined Plane

• The amount of work performed by lifting an object a certain vertical distance is the same as that performed by moving the object the same vertical distance, but across an inclined plane. The difference is that less force is needed to move the object across the inclined plane, but the object must be moved a greater distance.

Wedges

• A fifth type of simple machine is the wedge. It is usually a block of wood or metal that is wide at one end and narrows to a very thin edge at the other end.

• A wedge is a modified inclined plane.

• A wedge is not stationary, but instead moves in the direction of the applied force to split solid objects or to separate two objects from each other.

Screws

• Threads – The protrusions around the shaft of the screw are called threads even though they are actually a single, long inclined plane.

• A screw is a simple machine made up of an inclined plane wrapped around a cylinder.

• A screw will take less force to drive into an object but it will take more time.

Pulleys

• The pulley consists of a wheel that rotates freely around a stationary axle (not a attached like a wheel and axle).

• The outer rim of the pulley is grooved to hold a rope or chain.

• Single, stationary (fixed) pulleys do not magnify force but rather they are useful for lifting objects high overhead.

Mobiles

• Type of sculpture that is functions based on some of the same principles you have been studying.

• Mobile is an assembly of weighted objects suspended by a thread or wire.

• What type of simple machine does your mobile resemble?

• Where do you think the fulcrum is for each dowel?

Test review

• Know these words: effort, inclined plane, inertia, lever, newton, pulley, resistance, screw, speed, wedge

• Know the 6 simple machines, examples of each

• Know what work is and how it is calculated, friction, 3 classes of levers, compound machine