Key Idea.
Section 1
Unbalanced Forces Cause Change
When an object is floating or sitting still, the forces are balanced. But if one force becomes stronger than the other, the balance is broken. These are now unbalanced forces.
Unbalanced forces always cause a change in motion. If the upward magnetic force on the train stops, the downward pull of gravity takes over. The forces are no longer equal, and the train will start to fall.
Section 2
Evidence of Unbalanced Forces
We cannot see forces, but we can see what they do. If an object that was still suddenly starts to move, speed up, or turn, this is evidence that the forces have become unbalanced.
Observing a change in an object's motion tells us that a new or stronger force has acted on it.
Expand to review the lesson summary and core properties.
Section 1
Unbalanced Forces Cause Change
When an object is floating or sitting still, the forces are balanced. But if one force becomes stronger than the other, the balance is broken. These are now unbalanced forces.
Unbalanced forces always cause a change in motion. If the upward magnetic force on the train stops, the downward pull of gravity takes over. The forces are no longer equal, and the train will start to fall.
Section 2
Evidence of Unbalanced Forces
We cannot see forces, but we can see what they do. If an object that was still suddenly starts to move, speed up, or turn, this is evidence that the forces have become unbalanced.
Observing a change in an object's motion tells us that a new or stronger force has acted on it.