The Nature of Forces Presentation

THE NATURE OF FORCE

ESSENTIAL QUESTIONS

  • How is force described?

  • How are unbalanced and balanced forces related to an object's motion?

Definition of Force

  • Force Definition:
      - A force is defined as a push or a pull from one object to another.
      - A force may or may not cause movement depending on the context.

  • Measurement:
      - Forces are measured in newtons (N).

  • Gravity's Force:
      - Gravity exerts a force that pulls downward toward Earth’s center.

Types of Force

  • Applied Force:
      - This is when a person or an object directly pushes or pulls another object.

  • Normal Force:
      - The normal force is defined as the force that holds objects in place against gravity and other forces.

BALANCED FORCES

  • Characteristics of Balanced Forces:
      - When forces are balanced, the object stays still or continues to move at the same speed and in the same direction.
      - Balanced forces consist of two forces equal in size and acting in opposite directions on an object.

Examples of Balanced Forces:

  • Plates resting on a dining room table.

  • Cars halted at a stop light.

  • A plane flying at a constant speed and in a constant direction.

UNBALANCED FORCES

  • Characteristics of Unbalanced Forces:
      - Unbalanced forces always cause a change in motion. This change can occur in one of three areas:
        - Position
        - Direction
        - Speed
      - Unbalanced forces consist of two forces that are unequal in size and acting in opposite directions on an object.

Examples of Unbalanced Forces:

  • Sumo wrestlers of unequal strength.

  • Roller coaster cars accelerating down a hill.

  • Planets orbiting in space.

NET FORCE

  • Definition of Net Force:
      - Net force is the combination (sum) of all forces acting on an object.
      - Example Calculation:
        - Consider two forces where 3N is acting in one direction and 2N is in the opposite.
        - The net force can be calculated as:
          3N−2N=1N3N - 2N = 1N

THINK ABOUT IT

  • Bumper Cars as Examples of Unbalanced Forces:
      - When two bumper cars collide, the one that has the most force will continue to move forward, while the other car will be pushed away.
      - Predicting Collision Outcomes:
        - Students can consider which car will “win” in a collision based on the force exerted by each.

HOW DO UNBALANCED FORCES CAUSE A CHANGE IN POSITION OF AN OBJECT?

  • Example with Bowling Pin:
      - A bowling pin that is initially sitting still (balanced force). When a bowling ball hits the pin (unbalanced force), the pin falls over.
      - This demonstrates how the unbalanced force causes the pin’s position to change.

HOW DO UNBALANCED FORCES CAUSE A CHANGE IN DIRECTION OF AN OBJECT?

  • Example with Softball:
      - A softball approaches a batter (balanced force). If the batter hits the ball (unbalanced force), the ball then flies in the opposite direction.
      - The unbalanced force in this scenario is responsible for a change in the ball’s direction.

HOW DO UNBALANCED FORCES CAUSE A CHANGE IN SPEED OF AN OBJECT?

  • Example with Soccer Ball:
      - Consider a soccer ball rolling across a field (balanced force). When friction acts on it (unbalanced force), it slows down and eventually stops moving.
      - The unbalanced force contributes to a change in the ball’s speed.