Motion in a Straight Line: common misconceptions

If your child says… “Only tiny objects can count as points.”

Ask together

Does a carriage's length matter when tracking its travel between distant stations?

What’s true

The motion being studied decides which details matter.

If your child says… “Coming back subtracts the distance I travelled.”

Ask together

Can returning erase the outward part of the trip?

What’s true

Travel adds distance; each instant still has just one position.

If your child says… “A curved graph means a curved path.”

Ask together

Does the horizontal axis show time or another direction in space?

What’s true

This graph pairs position with time, not another spatial direction.

If your child says… “Negative acceleration always means slowing.”

Ask together

From −2 m/s to −6 m/s, does the speed grow or shrink?

What’s true

Negative acceleration can increase leftward speed when right is positive.

If your child says… “Displacement is the final position.”

Ask together

What must you add to the displacement to find the final position?

What’s true

Final position includes where the object started.

If your child says… “Gravity points upward while the ball rises.”

Ask together

If acceleration pointed upward, why would the rising ball slow?

What’s true

At the top, velocity vanishes while acceleration remains downward.

If your child says… “Twice the falling time means twice the distance.”

Ask together

During the longer fall, is the average speed unchanged or greater?

What’s true

From rest, constant gravity makes distance grow as time squared, ignoring air resistance.

If your child says… “Add speeds when both objects move the same way.”

Ask together

How does A's position change compared with B as B travels faster east?

What’s true

B gains on A, so A moves west relative to B.