Balanced & Unbalanced Forces
Plan and conduct an investigation to provide evidence of the effects of balanced and unbalanced forces on the motion of an object
What a learner can do afterwards
- Define balanced forces (equal in size, opposite in direction — no change in motion) and unbalanced forces (cause motion to change)
- Plan a fair test investigating how different force sizes affect an object's motion
- Use results as evidence to explain when forces are balanced versus unbalanced
The lesson
You already know how to draw force arrows for pushes, pulls, and friction. Now look at what happens when two forces act on the same object at the same time. If the forces are equal in size and point in opposite directions, they are balanced. Balanced forces cancel out, so the object's motion stays the same.
Now push the book harder. Your push grows to 8, but friction on the table only pushes back with 5. The forces are unbalanced, so the book starts to slide.
To test how force size changes motion, change only one thing, like how hard you push. Keep the same book and the same table every time. Then compare what happens.
Balanced forces are equal and opposite, so motion stays the same; unbalanced forces are unequal, so motion changes toward the bigger force.
Watch it
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.