Motion in a Plane: common misconceptions

If your child says… “Matching lengths mean equal vectors.”

Ask together

Do the outward and return moves point the same way?

What’s true

Equal vectors need matching magnitudes and directions.

If your child says… “The lengths always add.”

Ask together

Is the diagonal as long as the two sides together?

What’s true

After a turn, displacement is shorter than the total distance travelled.

If your child says… “Adding two unit vectors still gives magnitude one.”

Ask together

Is a square’s diagonal the same length as its side?

What’s true

Two perpendicular unit vectors add to a vector of magnitude $\sqrt{2}$.

If your child says… “Acceleration is velocity divided by time.”

Ask together

If a velocity component stays constant, what change would you divide by time?

What’s true

Acceleration uses velocity change.

If your child says… “Relative velocities always add.”

Ask together

As B overtakes A, does A move ahead of B or fall behind?

What’s true

Relative velocity subtracts the observer’s velocity from the object’s, using the same reference frame.

If your child says… “Sideways speed delays the fall.”

Ask together

At each matching time, which ball has fallen farther?

What’s true

Their vertical motions match.

If your child says… “Steeper always goes farther.”

Ask together

Does throwing straight upwards give horizontal range?

What’s true

At equal launch speeds, steeper throws do not always travel farther.

If your child says… “Unchanged speed means no acceleration.”

Ask together

Do the equal-length velocity arrows point the same way?

What’s true

Changing direction changes velocity.