# (Are they really that simple?!) What have we learned by doing labs and researching for our notes?

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(Are they really that simple?!)

What have we learned by doing labs and researching for our notes?

3 What is work? In science, the word work has a different meaning than you may be familiar with. #1 According to your text, work is done when a force causes an object to move in the direction of the force

4 Work or Not? According to the scientific definition, what is work and what is not?According to the scientific definition, what is work and what is not? –a teacher lecturing to her class –a mouse pushing a piece of cheese with its nose across the floor

5

Section 1 What is Work? Chapter 8

Section 1 What is Work? Chapter 8

Section 1 What is Work? Chapter 8

Section 1 What is Work? Chapter 8

Section 1 What is Work? Chapter 8

2. What is a “force”? A push or a pull What unit describes the size of a force? Newton (N) Measured with a spring scale

3. What is a machine? Something that makes work easier

4. How do machines make work easier? What do machines do? They change the size or direction of the force you apply

5. The work YOU do on a machine is called the Work input (input force) OR effort The work done by the machine on another object is called the Work output (output force) work input or effort work output

6. Machines DO NOT change the amount of work done. They only make it Work = F (force) X d (distance) easier. 12 J = 3N x 4m 12 J = 2N x 6m 12J = 1N x 12m

So, why use machines? Machines make work easier by changing the amount of force you exert distance over which you exert your force, or direction in which you exert your force However, the amount of work does not change! (W=Fxd)

TIME OUT!!! What is “mechanical advantage”? Jot this down at the bottom of your page! Mechanical advantage is the number of times a machine multiplies force. The greater the MA, the less effort required and the easier the work! And that’s a GOOD thing!

Inclined plane p. 145 Describe: Flat, slanted surface. An inclined plane makes work easier by letting you apply a _____________ force over a __________________ smaller longer distance The longer the ramp, the less effort required, the greater the mechanical advantage.

Inclined Plane: Examples ramp stairs hills boat ramps winding roads slides

Which inclined plane has the greater mechanical advantage? Why? Which machine above makes less work? Did I getcha? Work is the same; it just gets easier! Why? Shorter distance, more effort. 2m x 6N = 12J Longer distance, less effort. 6m x 2N = 12 J See your lab: Exploring Inclined Planes!

Wedge p. 146 Describe: Two inclined planes that move Like the inclined plane, the wedge needs a __________ input force over a _________________ small large distance

Which wedge has the greater mechanical advantage? The longer and thinner, the greater the mechanical advantage. That’s why sharper knives work better for cutting!

Wedge: Examples nails knives chisels axes paper cutter can opener needle/pin door stop

Screw p. 146 Describe: An inclined plane wrapped around a cylinder To turn a screw, a ____________ force over a ______________ is needed. smaller greater distance The closer the threads, the greater the mechanical advantage.

Which screw has the greatest mechanical advantage? Remember to look at the pitch-how close the threads are!

Screw: Examples screws light bulbs bolts jar lids C-clamps corkscrews drill bits

1 st class lever p. 141 Describe a lever: What is a fulcrum? A fixed point F LE: fulcrum The closer the fulcrum to the load, the greater the mechanical advantage. What’s in the middle? Resistance is AKA the load A bar that rotates at a fixed point *Change in direction

1 st lever: Examples see saw paint can opener crow bar door on hinges See Lab: Exploring Levers

2nd class lever p. 142 The output force does work on the load F L E: load (or resistance) What’s in the middle? Resistance is AKA the load *No change in direction

2 nd class lever: Examples wheelbarrow nutcracker garlic press See Lab sheet

3 rd class lever p. 142 The input force is AKA as your effort FL E : effort What’s in the middle? Resistance is AKA the load *No change in direction

3 rd class lever: Examples hammer broom fishing pole See Lab sheet

Wheel and axle p. 144 Describe: Two rounded objects that move together The larger object is the _____________ The smaller object is the ______________ wheel axle The larger the wheel, the longer the distance and the greater the MA.

Some wheels are NOT simple machines. They only reduce friction between two surfaces that are rubbing together. Let’s check your worksheet now to see if you understand the difference. reduce frictionwheel and axle Refer to your worksheet on wheels.

Wheel and axle p. 144 Gears are a special type of wheel and axle. They have teeth that interlock with other gears.

Wheel and axle: Examples faucet doorknobs steering wheels screwdrivers wrenches egg beaters

pulley p. 143 Describe: a grooved wheel that holds a rope or cable What are pulleys used for? lifting

Fixed pulley p. 143 To determine the MA of a pulley, count the support ropes that are pulling UP. MA = 1 This pulley only changes The direction of the force. See Lab: Exploring Pulleys

Movable pulley p. 143 Count the support ropes pulling UP to determine the MA. MA = 2 This pulley multiplies your force by two. You need half the effort. 20 N block 10 N force

Block and tackle pulley system p. 143 Count the support ropes to determine the MA. MA = 4 This pulley multiplies your force by four. You need one-fourth the effort. 20 N block 5 N force

What is the MA of the compound pulley we used in lab? MA = 3 This pulley multiplies your force by three. You need one-third the effort.

Pulley: Examples mini-blinds hoists in a garage flag poles sailing ships

A fixed pulley is shown. A fixed pulley can make work easier by A. Changing the size of the input force needed to lift an object B. Changing the direction of the force needed to lift an object C. Changing the size and direction of the force needed to lift an object D. Changing the amount of work that must be done

A fixed pulley is shown. A fixed pulley can make work easier by A. Changing the size of the input force needed to lift an object B. Changing the direction of the force needed to lift an object You pull down, object goes UP. MA = 1 C. Changing the size and direction of the force needed to lift an object D. Changing the amount of work that must be done NEVER!

This moveable pulley makes work easier by A Changing the size of the input force needed to lift an object B Changing the direction of the force needed to lift an object C Changing the size and direction of the force needed to lift an object D Changing the amount of work that must be done

This moveable pulley makes work easier by A Changing the size of the input force needed to lift an object You pull UP, the block moves UP. However, there are 2 ropes pulling UP, so the MA = 2. (change in force) B Changing the direction of the force needed to lift an object C Changing the size and direction of the force needed to lift an object D Changing the amount of work that must be done NEVER!!

The man in the picture is using a pulley system or a block and tackle. A pulley system can make work easier by A Changing the size of the input force needed to lift an object B Changing the direction of the force needed to lift an object C Changing the size and direction of the force needed to lift an object D Changing the amount of work that must be done

The man in the picture is using a pulley system or a block and tackle. A pulley system can make work easier by A Changing the size of the input force needed to lift an object B Changing the direction of the force needed to lift an object C Changing the size and direction of the force needed to lift an object Pull down, object UP. Two support ropes, MA = 2, half the effort force is needed to lift the block. D Changing the amount of work that must be done NEVER!

(Are they really that simple?!) Sure!! Now that you have learned all about them! Study your notes tonight!

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