Transitive verbs are action verbs that require a direct object to complete their meaning, while intransitive verbs do not require a direct object. Let's classify the verbs in the provided sentences as transitive or intransitive:
Heat expands metals.
Transitive (expands) - The verb "expands" requires a direct object "metals."
Metals expand on heating.
Intransitive (expand) - The verb "expand" does not require a direct object.
The driver stopped the car.
Transitive (stopped) - The verb "stopped" requires a direct object "the car."
The car stopped abruptly.
Intransitive (stopped) - The verb "stopped" does not require a direct object.
You must speak the truth.
Transitive (speak) - The verb "speak" requires a direct object "the truth."
You must speak loudly.
Intransitive (speak) - The verb "speak" does not require a direct object.
The boy is flying the kite.
Transitive (flying) - The verb "flying" requires a direct object "the kite."
The birds are flying in the sky.
Intransitive (flying) - The verb "flying" does not require a direct object.
The rider broke his arm.
Transitive (broke) - The verb "broke" requires a direct object "his arm."
The woodcutter felled a huge tree.
Transitive (felled) - The verb "felled" requires a direct object "a huge tree."
In summary:
Transitive verbs: 1, 3, 5, 7, 9, 10
Intransitive verbs: 2, 4, 6, 8