ACTIVE VOICE

Experts agree, most of the time, using active voice will make your writing more clear and direct.

What is voice?

All verbs have tense: past, present, future
(
This is a good way to recognize verbs--look for the time marker.)

Some verbs have voice, a particular relationship to the subject of the sentence.
It has nothing to do with tense. A verb in active voice can be past, present, or future.

What makes it active is its relation to the subject: 
        in active voice, the subject is performing an action named by the verb.

Active Passive

S        V            O

    S             V
Bob kicked the ball. The ball was kicked by Bob.
Here the subject performs the action Here the subject is passive, not performing any action (in fact receiving the action in this instance).

Do all verbs have voice?

Whether verbs have voice depends on the kind of sentence.

The three types of sentences, of which only one type has "voice":

1a. Joe shook the bottle.

1b. The bottle was shaken by Joe.

1a. Has a direct object. This is in active voice.
1b. When the direct object is made the subject, the verb is in passive voice.
2. Joe shook with anger

2. Has no direct object, so does not have voice

3. Joe is shaking with anger. 3. The verb links the subject to something that describes or renames the subject.  Does not have voice.

Formula for Active Voice                     Formula for Passive Voice:

agent             action                                                                                        action             agent

SUBJECT + VERB + OBJECT                         SUBJECT + "be" + VERB + [by Noun]

Joe             shook         the bottle.                             The bottle      was shaken             by Joe.


EXAMPLES:

1a. We will make the nozzle from a carbon-silicon composite. This is active.

1b. The nozzle will be made from a carbon-silicon composite. This is passive.

2a. Conventional booster rockets launch the vehicle into low-earth orbit. This is active.

2b. The vehicle was launched into low-earth orbit with conventional booster rockets. passive

3. Procedures for vectorization have been a major part of the research that was done by my team.

Here the verb "have been" links to something that renames the subject, so the main sentence is neither active nor passive.  
But the verb in the relative clause "that was done by my team" is passive.

4. It is seen that certain parts should be easily accessible for repair and maintenance.

Here the main clause is passive ("It is seen").
In the relative clause ("that certain parts should be easily accessible") the verb describes the subject ("parts") and so is neither active nor passive.

More sentences for discussion