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ZingPath: Newton's First Law

Balanced and Unbalanced Forces

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Newton's First Law

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Balanced and Unbalanced Forces

Physical Science

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Learners investigate the effects of balanced and unbalanced forces on an object.

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Now You Know

After completing this tutorial, you will be able to complete the following:

  • After completing this Activity Object, learners will be able to:
  • Predict that when two equal forces are applied in opposite directions to a stationary object, it does not move.
  • (LO 2) Predict that when two unequal forces are applied to a stationary object, it moves in the direction of the greater force.
  • Calculate the net force on an object and predict the direction of motion.

Everything You'll Have Covered

Simply stated, a force is a push or a pull on an object. If someone bumps into you and pushes you forward, or if someone pulls you up from a sitting position, you can easily feel that force. There are forces at work, however, that are not so noticeable. For example, do you feel the force of the floor pushing up on your feet? What about the force of gravity pulling you toward the Earth or the force of the atmosphere pushing down on you? All of these forces play a part in motion, though.

Newton's First Law of Motion states that an object at rest will stay at rest unless an unbalanced force is applied to it, and that an object moving at a constant velocity will continue to move at that velocity unless an unbalanced force is applied to it. Imagine two friends pushing against a box in opposite directions. If both are pushing with the same force, the forces are balanced, and the box will not move. Balanced forces result in a zero net force and cancel each other out. Now imagine the two friends pushing in on the box in opposite directions, but one exerts a greater force, and the box moves in the direction of the greater force. Unbalanced forces result in a net force and cause an object to move in the direction of the greater force. Finally, imagine the two friends pushing the box in the same direction. The combined forces cause the box to move in the direction they are both pushing. Again, unbalanced forces result in a net force and cause an object to move. The net force is the difference between the magnitudes of the two forces and can be expressed as follows: can be positive or negative values.)

The unit of force derived in the SI system is called a newton (N). You will not be surprised to learn that the newton is named for Sir Isaac Newton. It is equal to the amount of force required to accelerate a mass of one kilogram at a rate of one meter per second per second. It is represented algebraically as follows: To put the newton in perspective, 1 N is the force of Earth's gravity on an object with a mass of about 102 g, such as the proverbial apple that fell on Newton's head. The force of the Earth's gravity on a person weighing 68 kg (about 150 pounds) is approximately 667 N. The force that a professional baseball player's bat exerts on a baseball during a swing is about 27,000 N to 36,000 N or 27-36 kN.

Tutorial Details

Approximate Time 35 Minutes
Pre-requisite Concepts force
Course Physical Science
Type of Tutorial Experiment
Key Vocabulary acceleration, balanced forces, experiment