A force needs a direction
Magnitude, direction and unit of a force.
The cricket bat
A cricket bat hits a ball. If the bat hits harder, or from another side, the ball does something different.
To describe a force fully, what must we say?
What this lesson covers
The idea
A force is specified by its magnitude (its strength), its direction and its unit, and a change in magnitude or direction changes its effect; the SI unit of force is the newton, written with a small n, symbol N.
The cricket bat
A cricket bat hits a ball. If the bat hits harder, or from another side, the ball does something different.
To describe a force fully, what must we say?
- How strong it is and in which direction
- How strong it is, and nothing else
- What colour the object is
Change the force
Change the strength and the direction of the force.
Strength, direction, unit
The arrow gave two things: its length showed how strong the force was, and its pointing showed the direction. Changing either one changed the effect. Forces are measured in newtons.
A force is specified by its magnitude (its strength), its direction and its unit. A change in magnitude or direction changes its effect. The SI unit of force is the newton, written with a small n, symbol N.
Notes
A force has magnitude (strength), direction and unit. Changing the magnitude or the direction changes its effect. SI unit: newton (N).
Check yourself
Which things do we specify for a force?
What is the SI unit of force?
The magnitude of a force expresses its…
A force keeps the same magnitude but its direction changes. Its effect…
- Its magnitude alone. A force also has a direction, and a unit is needed to express the magnitude.
- Its magnitude, its direction and its unit — correct. Yes!
- Its direction alone. Direction is needed, but so are the magnitude, which expresses the strength, and the unit.
- The newton, symbol n. The name newton is written with a small n, but its symbol is the capital N.
- The kilogram, symbol kg. The kilogram is the SI unit of mass, not of force.
- The newton, symbol N — correct. Yes!
- strength — correct. Yes!
- direction. The direction is the way in which the force acts.
- unit. The unit is the newton. The magnitude tells how strong the force is.
- stays exactly the same. If the magnitude or the direction, or both, change, the effect of the force changes.
- also changes — correct. Yes!
- becomes zero. The force is still there, so it still has an effect, but a different one.