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Welcome! Today we are going to explore how balanced and unbalanced forces control how things move around us.
Forces are simply pushes or pulls acting on an object. When all the forces on an object are balanced, they cancel each other out, and the object's motion does not change.
Newton's First Law of Motion states that an object at rest stays at rest. Likewise, an object in motion stays in motion at a constant speed in a straight line, unless an unbalanced force acts on it.
When forces become unbalanced, the net force is no longer zero. This unbalanced force causes the object to accelerate, meaning it will speed up, slow down, or change direction.
Analyze the forces acting on a soccer ball resting on a flat grass field. Then, explain what happens to its state of motion when a player kicks the ball.
- Identify the initial forces: Gravity pulls the soccer ball downward, while the ground pushes upward with an equal normal force.
- Determine the initial state of motion: Because the downward gravity and upward normal force are equal in strength and opposite in direction, the forces are balanced. The ball remains at rest.
- Analyze the change: A player kicks the ball, which applies a sudden, strong horizontal force in one direction.
- Determine the new state of motion: The kick creates an unbalanced force because there is no equal force pushing back in the opposite direction. This unbalanced force changes the ball's motion, causing it to accelerate forward.
