Balanced and unbalanced forces, F = ma, weight, inertial mass, terminal velocity and third law pairs, with the practical that tests them.
What you will learn
- Find a resultant force and use F = ma
- Explain motion with balanced and unbalanced forces
- Explain terminal velocity
- Name a Newton's third law pair
Balanced forces, no change
First law: if the resultant force on an object is zero, its velocity does not change.
Still things stay still; moving things keep the same speed in the same direction.
So a car at a steady 30 m/s on a motorway has a driving force exactly equal to the resistive forces. It is not "a bigger force forwards". That is a classic wrong answer.
The rest of this lesson and its 9 practice questions are locked.
In this lesson
- Balanced forces, no change
- Unbalanced forces, acceleration
- Falling: terminal velocity
- Pairs of forces
- Try it: How big does the push need to be?
9 practice questions, marked as you go; about 25 minutes in all.
Key terms
Weight, Terminal velocity
In this unit: Forces and motion
Speed, velocity and acceleration, the graphs that show them, the equations of motion, Newton's laws and stopping distances.