Forces in two dimensions

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by David Kwan

| 22 QuestionsNote from the author:

This Formative is by: Mariana Garcia-Serrato

This assignment is meant to take at least three 50 min class periods, during which students will explore the concepts of balanced and unbalanced forces and explain how forces acting on an object cause a change in position (MS-PS2-2).

In hyperdoc fashion, it is arranged in different sections (Engage, Explore, Explain, Apply, Share). It makes use of two Flipgrids (open to all), as well as the Motion and Forces Phet sim and concludes with an assessment that asks students to revisit their original explanation from the Engage section.

How can one predict an object’s continued motion, changes in motion, or stability?

Engage

Look at the following image. Who do you think would win this Tug of War?

Explore - What is a Force?

Before you begin, remember Newton's first law. "An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

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1

What is a force?

A force is how you raise X-wings out of swamps.

Somethings that Jedi's use when they really focus.

A force is a push or a pull.

Nobody really knows.

2

1

What do we use to represent forces in a force diagram?

We use lines in different colors to show the magnitude of the force

We use arrows that represent the magnitude and direction of the force

We write them down on a separate piece of paper.

3

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What forces are acting on you right now?

The downward pull of gravity and the upward push of the surface of the Earth

Gravity and weather

None

Force = m x a

Measuring forces

A force meter is used to measure forces.Forces can be measured using a force meter. Force meters contain a spring connected to a metal hook. The spring stretches when a force is applied to the hook. The bigger the force applied, the longer the spring stretches and the bigger the reading.The unit of force is called the newton, and it has the symbol N. So 100 N is a bigger force than 5 N.

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Use a diagram to explain your understanding of balanced forces.

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Use a diagram to explain your understanding of unbalanced forces.

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Give an example of a balanced force; then explain what would happen if the force became un-balanced.

Explain

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Explain your understanding of combining forces.

Apply

For this portion of the assignment you will be using a Phet Simulator. Although the simulator is embedded here, I highly recommend that you open the activity in a new window and display them side by side on your screen. It will make your work much easier if you can see both things at once.

(Note: These tasks come directly from Sara Borenstein's lesson published on the Phet site)

Make sure you click on Net Force!

You will be recording your answers on the datacharts below. Please make sure to use the Text (T) tool.

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TASK 1

a. Place 2 people of the same size at the same distance away from the cart.

b. Make a prediction about the movement of the cart. (Record it on the data chart)

c. AFTER you have observed the actual movement, click on the sum of the forces box at the top right hand corner of the simulation.

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TASK 2

a. Place 2 people of the same size at different distances away from the cart.

b. Make a prediction about the movement of the cart.

c. AFTER you have observed the actual movement, click on the sum of the forces box at the top right hand corner of the simulation. Record the number in the data chart.

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TASK 3

a. Place 2 people of different sizes but the same distance away from the cart.

b. Make a prediction about the movement of the cart.

c. AFTER you have observed the actual movement, click on the sum of the forces box at the top right hand corner. Record the number in the data chart.

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TASK 4

a. Place 2 people of different sizes at different distances from the cart.

b. Make a prediction about the movement of the cart.

c. AFTER you have observed the actual movement, click on the sum of the forces box at the top right hand corner of the simulation. Record the number in the data chart.

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You and some friends are at the park . You find some rope and decide you’d like to play a game of tug-of-war. Unfortunately, there are 5 people so you can’t have an equal amount of people on each side. One of your friends suggests that the two biggest people should be on one side, while the three smaller people should be on the other side. Do you think this is a fair way to split up teams? Why or why not? Explain your answer using your observations from the simulator.

Share

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What causes objects to move or stay still?

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Balanced forces cause a change in motion.

True

False

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You exert a force of 120 N on a desk. Your friend exerts a force of 150 N in the same direction. What net force do you and your friend exert on the desk?

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You exert a force of 120 N on a desk. Your friend, not very brightly I may add, decides to push the desk from the opposite direction, exerting a force of 150 N. What net force do you and your friend exert on the desk? What will be the direction of the movement?

17

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If gravity pulls you towards the centre of the Earth, why don't you fall through the pavement?

Because gravity doesn't act through pavements

Because the pavement exerts an equal force in the opposite direction

Because gravity runs out

Because the atmosphere pulls you up

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All of the following statements are true, except...

A moving object carries on moving until a force stops it

A moving object eventually runs out of force and slows down

A moving object travels in a line until a force changes its direction

An object is at rest because all the forces around it are balanced

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Calculate the net force and describe the direction of movement. (i.e. The weelbarrow will move to the ______ with a net force of _______ N)

20

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Will this rocket be able to lift off? Explain your answer using your net force calculations

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When finding net force, why must you know the directions of the forces acting on an object?

22

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Go back to the explanation you provided at the beginning of this assignment (Tug of War Flipgrid). Label the forces needed ensure that your original explanation was in fact correct.

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