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What are Forces? October 20, 2014

Forces

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Powerpoint on forces and friction/gravity 5th grade

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Page 1: Forces

What are Forces?

October 20, 2014

Page 2: Forces

What forces do you think are acting on you right now while you’re sitting in your seat?

Page 3: Forces

There are forces acting on you all the time whether you know it or not!

• Gravity is pulling you down • The ground is pushing you up • Air is squeezing you from every

direction • Your body is pushing back at the air

Page 4: Forces

When forces are balanced, they cancel out and you don’t notice them. But when forces

don’t balance, things happen…

THINK! What would happen if we took the force of gravity away?

Page 5: Forces

A force is a PUSH or a PULL

• Forces can cause an object to move, change speed, change direction, change shape, or stop

• Forces have size and direction

Page 6: Forces

• When you drop your pencil, gravity is pulling it to the ground

• When you are walking around, your feet are pushing down onto the ground

Page 7: Forces

Force Facts

• Measured in Newtons (N) • Always act in pairs • Cannot be seen, but the effect can

be seen • Measured using a spring scale

Page 8: Forces

Measuring Force

• How many Newtons will it take for me to drag your science binder across the desk?

Page 9: Forces

Net Force

Net force: the size of all the forces acting on an object • If two forces acting on an object are

in the SAME direction, you ADD the forces together

• If two forces acting on an object are in the OPPOSITE direction, you SUBTRACT the forces

Page 10: Forces

Written with a magnitude and direction

Ex: Force Net = 30 N

Page 11: Forces

Net force =

50 N 75 N

If two forces acting on an object are in the SAME direction, you ADD the forces together

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Net force =

500 N

100 N

If two forces acting on an object are in the OPPOSITE direction, you SUBTRACT the forces

Page 13: Forces

Balanced Forces

• Forces that cancel each other out• Net force = ZERO • There is no change in motion

Page 14: Forces

Balancing your science textbook on your desk

Force net =

Page 15: Forces

Net force =

Page 16: Forces

Unbalanced Forces

• When forces acting on an object do not cancel out

• Net force does not = zero• Produce a change in motion

Page 17: Forces

Net force =

Page 18: Forces

Checkpoint

1. What is the unit used for measuring a force?

Newtons

2. What tool is used to measure forces?

Spring Scale

Page 19: Forces

3. Find the net force

950 N 625 N

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Page 21: Forces

Review

1. Find the net force

600 N 600 N

Page 22: Forces

2. Find the net force

525 N 50 N

Page 23: Forces

Forces that act against motion…

If you kick a soccer ball on grass, what will start to slow it down?

Page 24: Forces

The enemy of motion

• Friction: force that occurs when 2 objects rub against each other

• Always acts in the direction opposite to the direction of motion

• Will slow the motion of an object or stop it

• Creates heat

Page 25: Forces

• Every object causes friction, some more than others

• It may look smooth, but it is covered in tiny bumps and dents

Page 26: Forces

• Friction can be beneficial

• Everyday life would be a lot different without it

• THINK! What would happen if the floor in the classroom was ice instead of carpet?

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Page 28: Forces

When would decreasing friction be beneficial?

Page 29: Forces

Is it possible to pick up a bottle full of rice with just a pencil?

YES!

Page 30: Forces

4 Types of Friction

• Static friction• Sliding friction • Rolling friction • Fluid friction

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Fluid Friction- Air Resistance

• Caused by friction of the air against an object

• Objects with more surface area experience greater air resistance and move more slowly

Page 32: Forces

Gravity

• Force that pulls objectstowards each other

• Law of gravitational force: The force of gravity depends on the distance between the objects and their masses

Page 33: Forces

Which objects have the greatest force of gravity?

A B C D

A and CD and B B and C A and D

Page 34: Forces

• Mass: the amount of matter in an object (g)

• Weight: measure of the force of gravity on an object (N)

Page 35: Forces

• All objects fall at the same rate towards the earth because gravity pulls on every object the same amount

• Air resistance slows objects down

What would hit the ground first, a pencil or a ball?

What about a sheet of paper and a balled up sheet?

Page 36: Forces

An object’s weight can change if you went from the earth to the moon, but

your mass would stay the same.

Ex: Gravity on moon is 1.622 m/s2

Page 37: Forces

THINK! What would happen if we drop a feather and a hammer on earth?

What if we were on the moon?

Hammer-feather drop

What is happening?

Page 38: Forces

Zero G Experience

http://www.gozerog.com

Page 39: Forces

Checkpoint

1. Is your mass the same on earth and the moon?

2. Is your weight the same on the earth and moon?

3. What forces will effect a soccer ball that has been kicked?