Welcome! Today we will explore how forces change the way objects move.
Newton's First Law says an object stays at rest or keeps moving at a constant speed unless an unbalanced force acts on it. When forces are balanced, the net force is zero and motion does not change.
Let us analyze a box pushed by two people. If both push with equal force in opposite directions, the forces are balanced and the box stays still.
Now, imagine one person pushes harder. The forces become unbalanced, creating a net force that causes the box to speed up to the right.
✏️ Worked example
A soccer ball is rolling across a grass field at 5 m/s. Friction pushes against it with 3 N of force, while no one is kicking it (0 N forward). Analyze the effect of these forces on the ball's motion.
1. Identify the forces acting on the ball: Forward force = 0 N, Friction force = 3 N backward.
2. Calculate the net force by subtracting opposing forces: 0 N - 3 N = -3 N (3 N backward).
3. Determine if forces are balanced: Since the net force is not zero, the forces are unbalanced.
4. Apply Newton's First Law: An unbalanced force changes motion. The ball will slow down and eventually stop.
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