Balanced and Unbalanced Forces

7th Grade Science

Physics

Balanced and Unbalanced Forces

Teacher PageObjectivesStudents will

identify net force.

identify balanced and unbalanced forces.

describe how forces affect motion.

Materials

desk or object that can be pushed by two studentsProcedure

Have students demonstrate the concepts of

unbalanced forces in the same direction.

unbalanced forces in opposite directions.

balanced forces in opposite directions.

1. Two students push the desk at the same time and in the same direction. Ask: What is the net force acting on the desk? Students should write their responses in a journal. (The force of the first students push added to the force of the second students push.)

2. One student pushes with one hand while the other pushes with two hands. Ask: How would you calculate net force? (Find the difference between the force of the first students push and the force of the second students push.) Ask: What happens to the desk when the forces acting on it are unequal? (The desk moves in the direction of the greater force.)

3. Two students push with equal forces acting in opposite directions. Ask: What is the net force acting on the desk? (zero) Ask: What happened to the desk when two equal forces push it from opposite directions. (The desk did not move.)

4. Have students identify other objects acted upon by equal and unequal forces and sketch the objects with arrows that represent the direction and strength of forces.

Name: ________________________________________Date: _________________Period: _____Balanced and Unbalanced Forces

Student PageObjectives identify net force.

identify balanced and unbalanced forces.

describe how forces affect motion.

Materials

desk or object that can be pushed by two students

Procedure

Demonstrate the concepts of

unbalanced forces in the same direction.

unbalanced forces in opposite directions.

balanced forces in opposite directions.

1. Two students push the desk at the same time and in the same direction.

a. What happened to the table?

b. How would you calculate net force for this example?

c. Is the force acting on the table balanced or unbalanced?

2. One student pushes with one hand while the other pushes with two hands.

a. What happened to the table

b. How would you calculate net force for this example?

c. Is the force acting on the table balanced or unbalanced?3. Two students push with equal forces acting in opposite directions.

a. What happened to the table

b. How would you calculate net force for this example?

c. Is the force acting on the table balanced or unbalanced?

4. Have students identify other objects acted upon by equal and unequal forces and sketch the objects with arrows that represent the direction and strength of forces.

5. Calculate the net force in newtons exerted on the objects.

a. 5 N

2N

Net force =___________________

Is the force balanced or unbalanced?

_____________________________

Net Force = _________________

3N

3N

b.

Is the force balanced or unbalanced?

_____________________________

6. In order for you to do work on an object, the object must move some distance as a result

of your force. The amount of work done on an object can be calculated by multiplying

force times distance. Work is measured in joules.

Work = Force x Distance

Example: How much work has been done if a refrigerator is moved 2 meters with a force of 15N?

Work = force x distance

Work = 15N x 2 meters

Work = 30 joules

a. Jack pushes a lawn mower with a force of 8N over a distance of 25 meters. How much work does Jack do?

b. You exert a force of 1.5N to lift your backpack off the floor. How much work do you do if you

lift the backpack 2 meters?PAGE SBISD

Fall 2008