Tension Force

Learning objectives

• I can use newton's second law of motion to find the tension force acting on a dynamic object by analyzing the forces in x and y components.

Success Criteria

1. Make a sketch.
2. Draw a FBD for each object in the system - label all the forces.
3. Resolve forces into x and y components.
4. Use ∑ F_X = ma and ∑ F_Y = ma ( depends on the movement)
5. Keep track of the force directions and decide on a coordinate system so you can determine the sign (neg or pos) of the forces.
6. Develop equations using the second law for the x and y directions.
7. Solve the equations.

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Important Vocabulary�

• Normal Force
• Contact Force
• Tension
• Coefficient of Friction

Starter

• In your own words, describe this image?

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• Predict what will happen if the rope was cut?

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• How could four ropes balance the movement of the body?

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Have I got a tension headache!

• Tension, T, is the “contact force” for pulling objects
• Tension is a real force—you can measure it by cutting the string and inserting a force scale

TENSION

Tension is real—it can be measured.

Tension Problem

• Given, M1, M2, and F
• What is acceleration?
• What is the Tension, T in the line?
• What is the force on each block?

IMPORTANT:

Blocks move together, so each has the same acceleration “a” and speed “v”.

Check work: Look a limits of large and small M1, M2.

Pulleys: the beginnings of technology.

A pulley changes the direction of Tension

Compare the tension in the left and right cases.

1. The left is higher.
2. The right is higher since the mass is double.
3. They are the same.

Simplest pulley system.

What happens to the tension?

1. It is the same in both cases, the bucket mass doesn’t change.
2. The tension doubles in the right side.
3. The tension is reduced by ½ in the right side.

The “bosun’s chair” problem.

Accelerating blocks: more of a challenge

Given M2, M1 and g.

What is a?

What is the tension?

What are the forces?

(ignore friction)

Accelerated blocks and tension.

CAUTION: The TOTAL force on M2 is NOT JUST THE WEIGHT!

Freebody diagram

NOTE: Why is the diagram for mass 2 correct? Isn’t it moving in the y axis?

a

a

Accelerating tethered blocks.

Block on the table.

Block dropping down.

a

Does this make sense? Check it by looking at limits of M2.

Tethered blocks: add one more!

T₁

T₂

T₂

M₃g

Add all three equations together.

Do on “board” then reveal