Nov. 29, 2018 You need: Clean paper (2) / pencil Newton’s foldable Newton’s 2nd law practice problems Warm Up: What does Newton’s 3rd law say? Draw a sketch, too. I CAN: investigate simple machines

Newton’s 3rd law Action-reaction For every action FORCE there is an equal and opposite reaction FORCE. Try showing it with a sketch like this cool site’s interactive Newton’s cradle.

What is Momentum? Momentum is a measure of how much motion object has. It is affected by mass and velocity. The heavier an object is, the more momentum it has. It’s easier to stop soccer ball coming towards you at 20 m/s than a car coming at 20 m/s. It’s easier to stop car travelling at 1 km/h than a car travelling 60 km/h!

Conservation of Momentum When objects collide, their total momentum is conserved (stays the same), unless outside forces act. The total amount of motion coming into a collision will also come out of the collision.

Magnet Lab On your paper – write observations!! Play – SAFELY (away from electronics) for 2 minutes. Be sure to share with your table partners. Students should be able to tell that the magnet is attracted or PULLS to metal items – though not all. I use their observations to share ideas and explanations and then draw an atom and bring in positive and negative. We know that opposites attract…this is the best segue to the next part…

Magnet Lab On your paper – write observations!! Play – SAFELY (away from electronics) for 2 minutes. Be sure to share with your table partners. BUT – this time try to find a way to make the magnet PUSH. Write and share observations. Students should be able to tell that the magnet is attracted or PULLS - so how would one get the magnet to PUSH?

Build a Tab Book Foldable Use two sheets of paper (we used green and white). Fold both in half – hotdog style to find the middle. Cut both down the middle. Take the four long ½ sheets and arrange them so that you have alternating color (green/white, green/white).

Build a Tab Book Foldable Once they are alternating colors, place each one so that it is about 2 cm above the next. (front piece highest) Pull the top half down and towards you – to create the tab book. Be careful, you should have 8 tabs, but the middle tabs will likely be the same (ex: white/green/white/green/green/white/green/white) We’ve done these before – but they always need a little guidance. I provide “models” of the product and typically go to each table. If none have gotten it on his own, I can usually help one and have them help the others at the table.

Simple Machines (Making work easier…phew!)

Simple Machines Foldable 8 Simple Machine Notes 7 Lever 6 Pulley 5 Wheel & Axle 4 Wedge 3 Screw 2 Inclined Plane 1 Simple Machines Simple Machines By John Smith Line up your papers about 1-2 cm apart, so that you see “5, 6, 7, 8” along the bottom. Fold the papers over so you see all 8 numbers in a row.

Simple Machines Foldable 8 Simple Machine Notes 7 Lever 6 Pulley 5 Wheel & Axle 4 Wedge 3 Screw 2 Inclined Plane Draw & Describe: A sloped surface connecting a lower level to a higher level. Examples: A boat ramp, wheelchair ramp,propeller, ladder/stairs Simple Machines Foldable On each tab, draw and describe that type of simple machine. Then give 2-3 examples.

What are MACHINES? Most people think of complex, technical, or electronic gadgets with motors…, but machines can be much SIMPLER. A machine is any device that lets you do WORK in an EASIER or BETTER way. Basically: Simple machines make work EASIER.

How do machines do work? Machines make work easier by changing 3 things about the FORCE you exert to do work: AMOUNT OF FORCE you exert DISTANCE over which you exert force DIRECTION in which you exert force

What are SIMPLE MACHINES? There are only 6 basic simple machines that make work easier: Inclined Plane Wedge Screw Lever Wheel & Axle Pulley

COMPOUND MACHINES Compound Machines – are made of combinations of two or more simple machines. For example, a simple can opener is a combination of 3 simple machines: Lever Wheel & axle Wedge

WORK & SIMPLE MACHINES Simple machines DON’T change the amount of WORK done! (They change the size, distance or direction of your FORCE!) WORK IN = WORK OUT* (*usually machines lose a bit of work due to FRICTION…)

INCLINED PLANE An inclined plane is a flat, sloped surface. It connects a lower level to a higher level. You use less force over a longer distance to raise a load to a higher level. Input Force Output Force

INCLINED PLANE: Examples Ramps (Boat ramps, wheelchair ramps) Propeller Ladders/Stairs

SCREW A screw has a “thread” or “groove” wrapped around a central cylinder. While turning, it converts a twisting force into a forward or backward force. Input Force Output Force

SCREW: Examples & Uses Screws can holds things together or lift materials. Screws Screw top lids for jars/bottles Light bulb Swivel stools/chairs

WEDGE A wedge has slanting slides that meet at an edge – it splits material apart. It changes force in one direction into a splitting force that acts at right angles to the blade. Input Force Output Force

WEDGE: Examples & Uses Ax, Knife, etc. Zippers Used in all cutting machines (to split materials apart)

WHEEL & AXLE The wheel is locked to the central axle – when one turns, so does the other one. A short powerful force at the axle, will move the wheel’s edge a long distance. A long motion at edge of wheel, moves the axle with great force. Output Force Input Force Output Force Input Force

WHEEL & AXLE: Examples & Uses Screwdriver Windmill Cars/Bicycles Rolling Pin Door Knob Fan

PULLEY A pulley is a grooved wheel with a rope, used to raise/lower/move a load. Pulley systems change the direction and/or decrease the input force so you can move heavier loads. Output Force Input Force Output Force Input Force

PULLEY: Examples & Uses Cranes Raising a flag on a pole Window Blinds Raising a sail on a boat Clothesline

LEVER A lever is a bar that pivots or rotates on a point (called a fulcrum). Levers may change the size, distance or direction of the force.

LEVERS: Examples & Uses First Class Levers: Scissors, See-saws, Pliers Second Class Levers: Staplers, Nutcrackers, Wheelbarrows Third Class Levers Shovels, baseball bats, tweezers

Machines make work easier by changing 3 things about the FORCE: The amount of force The distance of the force The direction of the force

Machines make work easier by changing 3 things about the FORCE: The amount of force (eg. A ramp lets you lift a heavy object with LESS force)

Machines make work easier by changing 3 things about the FORCE: The distance of the force (eg. A baseball bat lets you move your arms a short distance, but move the end of the bat a large distance).

Machines make work easier by changing 3 things about the FORCE: The direction of the force (eg. The pulley on a set of window blinds lets you move the blinds UP with a DOWNWARD pull.

How do machines make work easier? In your science notebook, write the following questions: When you add pulleys to a system what happens to the force you need to do work? How can we change a lever to make it easier to lift a heavy weight?

What is the mechanical advantage of a machine? A machine’s mechanical advantage is the number of times a machine increases a force exerted on it. Mechanical = Output Force Advantage Input Force

What is the mechanical advantage of a machine? You exert 10 N of force on a can opener. The can opener exerts 30 N of force on the can. What is the mechanical advantage? Mechanical = Output Force = 30 N Advantage Input Force 10 N Mechanical Advantage = 3

What is the efficiency of a machine? The EFFICIENCY compares: the work you put IN to the work the machine puts OUT. An IDEAL machine is 100% efficient. INPUT WORK = OUTPUT WORK In the real world, some input work is always lost due to FRICTION between the moving parts of the machine.

What is the efficiency of a machine? EFFICIENCY = Output Work x 100% Input Work You mow the lawn with a rusty lawn mower. You do 50,000 J of work on the lawn mower but only 25,000 J go to cutting the lawn. What is the efficiency of the lawn mower?

What is the efficiency of a machine? You mow the lawn with a rusty lawn mower. You do 50,000 J of work on the lawn mower but only 25,000 J go to cutting the lawn. What is the efficiency of the lawn mower? EFFICIENCY = Output Work x 100% Input Work Efficiency = 25,000 J x 100% 50,000 J Efficiency = 50%

Try the rest of the practice problems on your own… Mechanical = Output Force Advantage Input Force EFFICIENCY = Output Work x 100% Input Work