Thursday October 28th

Agenda:

• Homework

• Presentations

• Power Point

• Reflection

Please have your homework out so I can stamp it before class starts!

Creating an Explanation10/28/10

15

Summary:

• Air Resistance: the opposing push that works against the pull of gravity aka “drag”

• Force: a push or a pull on an object (ex: gravity, air resistance, buoyancy, friction)

Whirligig Science - Gravity

What is a force?

• a push or a pull

• every force has an opposing force that acts in the opposite direction

Identify the two forces at work in the picture.

• when there is no movement, it means the opposite forces are equal

Predict what will happen if you let go? Why?

Gravity

(pulling down)

Hands/Fingers

(pushing up)

When you release the whirligig, the greater force (gravity) pulls it to the ground.

What happened to the opposing force? Does it still exist?

• YES! Every force has an opposite force pushing or pulling on it in the other direction.

What is the other force acting on the whirligig?

Which force is greater? How do you know?

Gravity

Air Resistance (drag)

The blades of the whirligig are falling through the air

and bumping into air molecules along the way. These collisions create a push against the bottom

side of the blades.

Can you feel the air molecules around you?

Gravity

As air molecules collide with the wing,

drag is created

Push Against Gravity – Air Resistance (Drag)

Feel the Air Resistance on Your Hand

• Hold your hand out with the palm facing down.

• Move your hand back and forth.

• Describe what you are feeling.

• Explain why.

• Now hold your hand out with the palm facing left or right.

• Compare the feeling of moving it back and forth and holding it still.

• How does it feel differently if you move your hand faster? Why?

• What difference did you feel when you moved your hand parallel to the floor compared to perpendicular to the floor? Why?

• Draw a picture explaining push and pull of the air particles on your hand. Be sure to include each of the opposing forces with arrows.

Think – Pair - Share

Remember back to the book support challenge. We learned that if something above Earth is not supported then it will fall toward Earth because of the gravitational pull between Earth and the object.

How does gravity pull on a whirligig?

Think – Pair - Share

When you move your hand through the air, you can feel your hand interacting with the air resistance as it pushes in the opposite direction.

How does air resistance affect the whirligig as it moves through the air?

Think – Pair - Share

When you add paper clips to the stem of the whirligig, the mass of the whirligig increases.

How does the change in mass affect the way the whirligig fall?

Think – Pair - Share

When you add paper clips to the stem of the whirligig, the mass of the whirligig increases.

How does the change in mass affect the way the whirligig fall?

When you measured the seconds it took for the whirligig to fall, are you measuring quickness or something else?

Mass attracts mass. this attraction increases and becomes noticeable because the force due to the gravity increases with the mass.

Think – Pair - Share

When your palm was facing the floor you didn’t notice much air resistance, but when your palm was facing the direction you were moving your hand, you noticed the air going around your hand.

What changed when you made the blades on your whirligig longer? Predict what would happen if you made the blades longer and wider.

When you add paperclips to the whirligig you are increasing the

mass of the whirligig.

However, if we were to drop a whirligig with one paperclip and

another with five paperclips from the same height in an air-free environment, they would reach the ground at the same

time.

It is not just the mass of the object but also the air it is

moving though that affects how fast an object falls.

Changing the Forces Due to Gravity and Air Resistance

Create an Explanation

After scientists get results from an investigation, they try to make a claim. They base this claim on what their evidence shows. They also use what they already know to make their claim. They explain why their claim is valid.

The purpose of a scientific explanation is to help others understand the following:

o What was learned from an investigationo why the scientists reached this conclusion

Later, other scientists use this explanation to help them explain phenomenon, and to help predict what will happen in other situations.

You will do the same thing now. DIV 58

Creating an Explanation10/28/10

15

Summary:

• Air Resistance: the opposing push that works against the pull of gravity aka “drag”

• Force: a push or a pull on an object (ex: gravity, air resistance, buoyancy, friction)

• Evidence: data collected in the investigation and patterns in the data

• Science Knowledge: what you know about how things work, gathered from reading,

research and discussion. It helps you understand why a claim is true.

Wrap Up

o Summaryo Turn in Homeworko Flipper on Spread 14 –

Homework reading papers

Work Time/Wrap Up

o Homework: Due Friday 10/29oRead pages 59 – 61 in textoWorksheet – Create Your

Explanation

o Summary