1Simple and Complex Machines

Adapted by Mr. Zindman

I love machines mon ami!

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Balanced forces are forces that are equal in magnitude, but opposite in direction. Unbalanced forces are forces that are opposite in direction, but unequal in magnitude.Work is a transfer of energy to or from an object by applying a force over a distance. force.Simple machine is a device that makes work easier by changing the amount or direction of aPulley is a simple machine that consists of a wheel with a groove along the edge to hold a rope. Lever is a simple machine that consists of a rigid bar that moves around a pivot point called a fulcrum. Inclined plane (ramp) is a simple machine that reduces the force needed to lift an object to a height.Wheel and axle is a simple machine that consists of a large wheel with a smaller cylinder (axle) going

Friction is a force that resists motion.Complex machine consists of two or more simple machines.

•Vocabulary

through its center.

Do not worry, your teacher will go over

these vocabulary

words in the presentation!

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What do hitting a ball with a bat, lifting the top off a box, and riding a bicycle have in common? Each action requires a force. A force is a push or pull on an object that changes the way that the object moves. You push the ball with the bat, pull the top from the box, and push the bicycle pedals to move forward. All these

actions require a

force!

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As you stand on Earth, the force of gravity pulls you down.Your weight is a measure of the force of gravity. Earth's surface pushes you up. These are balanced forces-equal in magnitude,but opposite in direction. Balanced forces cause no change in motion. To start an object moving or to change the speed of a moving object, an unbalanced force must act on it. Unbalanced forces are forces that are opposite in direction, but unequal in magnitude. If there is no unbalanced force, an object will remain at rest or continue to move at a constant speed.

The force of gravity

keeps your feet on the

ground!

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When you exert a force on an object and the object moves, you do work. Work is transferring energy to or from an object by applying a force over a distance. If you push on a wall, you don't do any work because the wall doesn't move. If you use the sameforce to push a shopping cart, you do work. You can figure out how much you do by multiplying the force that you use by the distance that the object moves.

work (W) = force (F) x distance (d)

Force is measured in newtons (N). Work is energy, measured in joules (J). For example, if you use a 5 N force to lift a box 2 m,you do 10 J of work.

When you move an object, you do work!

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Most machines, no matter how complex, are combinations of two or more simple machines. Simple machines make a task easier by changing the direction or amount of force needed. Some simple machines also change the distance or the speed for the force needed to do work. Simple machines are often used to transfer mechanical energy from one object to another.

Machines change the direction of

the force that is applied to

an object

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For example, lifting a box onto a shelf over your head is difficult. The pulley in the picture makes it easier. A pulley consists of a wheel with a groove along the edge to hold a rope.

You still have to do the same amount of work, but pulling down on the rope is easier than lifting the box up. The pulley changes the direction of the force. The pulley also transfers mechanical energy from your hands to the box.

A pulley is made up of a wheel with a

groove to hold a rope.

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You can use another simple machine to pry up a heavy object, such as a rock. A lever is a rigid bar that pivots around a fixed point called the fulcrum. The closer the fulcrum is to the object, the less force you need to move the object. But you have to push the end of the lever through a greater distance than the object moves. You use less force through a greater distance, so the amount of work is the same for whatever force and distance are involved. Levers can be used to move a heavy object, open a paint can, pry out a nail, or make a teeter-totter. Levers transfer mechanical energy from the object on one end of the lever to the object on the other end of the lever. Force

Fulcrum

A lever lifts using a fulcrum

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A ramp, or inclined plane, decreases the force you need to lift an object, but it increases the distance you must move the object. Suppose you have to lift a heavy box and put it in the truck bed in the picture. Gravity pulls the box down, so you have to exert a force greater than the weight of the box to lift it. But you only have to exert the lifting force over a short distance. You use less force to push the box up the ramp, but you have to exert the pushing force over a long distance. You do the same amount of work by using the ramp or by lifting the box because you trade force for distance.

An incline plane decreases the force you need to lift an

object.

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A wheel and axle has a large wheel with a smaller cylinder,called an axle, running through the center. A doorknob is a wheel and axle. Imagine trying to open the catch on a door by turning a little cylinder with the diameter of a pencil. The cylinder is the axle. The doorknob is the wheel. It takes much less force to turn the doorknob than the axle. Force applied to the wheel is multiplied when it is transferred to the axle. The larger the diameter of the wheel, the less effort you need to turn it, but you have to move the wheel a greater distance to get the same work done. The faucet on a sink, a Ferris wheel, gears, and the wheels on a bicycle are examples of a wheel and axle. You use a wheel and axle when you turn the handle on a pencil sharpener or wind up a toy car.

Hey, Hey Hey! Force applied a wheel is

multiplied when it is transferred to the axle.

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Wheels also reduce the amount of force needed to move a heavy object, such as a car. If you push a box across the floor, the entire bottom of the box is in contact with the rough floor. The floor exerts a force called friction that resists the motion of the box. If you put wheels on the box, the smooth axle rotates more freely. That means there is less friction. Friction affects all machines because some surface on each machine rubs against another surface. Machines can be made more efficient by reducing the friction between these surfaces. One way to reduce friction is to use lubricants such asoil, wax, or grease on the touching surfaces.

Wheels also reduce the amount of force needed to move a

heavy object

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The other two simple machines are based on the inclinedplane. A screw is an inclined plane wrapped around a cylinder. You have to turn the screw many times, but you use less force than pushing the screw straight into the wood. A wedge is an inclined plane that moves. It usually has two angled surfaces back to back. An axe, a chisel, and a knife are examples of Wedges.

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More complicated machines, called complex machines, can be built from combinations of simple machines. For example, a catapult uses a large lever to hurl a weight, a pulley to pull the lever down, and wheels and axles to move from place to place. A bicycle uses wheels, pulleys, and levers to move. Also, bicycle gears are wheels that are ringed with small wedges.

Complex machines, can be built from combinations of

simple machines.

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Mr. Peebles is going to like this!