1. Do you consider psychology a science? why
Yes. It DOES employ the scientific method. Research psychologists/psychiatrists notice a fact, come up with ideas as to why that fact is so, come up with tests to see if their ideas are correct.
For example (simplified, eliminating credit for all the years of research it took), psychologists saw people who were alternately depressed and very excitable (manic-depressive, aka bipolar).
They hypothesized that it was caused by a chemical imbalance.
They devised tests to see if there was a chemical that could eliminate the symptoms.
They found that lithium did.
Using the scientific method, they figured out how to control the symptoms of manic depression.
Of course, there are other areas where a modified version of the scientific method is used - i.e. they don't have a fact and are hypothesizing as to what the outcome of certain interactions will be. i.e. "What will happen if instead of giving the rat food when it presses a button, we give it a shock instead. I think the rat will stop pressing the button. I'll design an experiment in which I hook a zapper up to the button and then send the rat in."
2. Is Psychology more or less of a science in comparison to other fields such as physics, biology? why
No. The difference is that it's a NEWER science. People tend to think of psychology as a non-science because its track record of being right is not overly positive right now. Pretty much everything Freud ever said is crap, for example. It's been wrong a lot.
But let's not forget that other sciences were the same way in their infancy. Early chemists spent tons of time trying to make gold out of lead. Early astrophysicists thought the sun revolved around the earth, and so did the universe. Early medical science believed disease was caused by witchcraft or an imbalance of bodily humors for which bleeding was prescribed.
Frankly when you hold psychology up against the early stages of other sciences, it's doing pretty damn well
3. What are the strengths and weaknesses of psychology?
The main strength is that, especially lately, it treats mental illness as what it is - an illness. We don't lock people away from society and consider them freaks because they have the flu, yet in very recent years we did that because they had an anxiety disorder.
The weakness is that there are still lots of different theories floating around out there, and it can be hard to know what is right.
Another weakness is that you do not have to be licensed to be a therapist. Any one of you can hang a shingle out right now and call yourself a therapist and charge people to "help" them with their problems, even if you don't know anything about psychology. That's lead to a lot of charlatans running around pretending to know what they're talking about, and the public doesn't know the difference. Then when patients aren't helped because their "therapist" is full of crap, they blame psychology as a field rather than the shyster they've been going to.
A third weakness is that psychiatrists are allowed to practice in the field. Most people don't realize it, but psychiatrists know much less about psychology than psychologists do. Psychiatrists are medical doctors. They go to med school. They become a psychiatrist by doing their internship with a psychiatric unit.
People go to psychiatrists thinking they'll get a good psychological treatment, but really all the psychiatrist is gonna do is throw drugs at them, and that's the main weakness in the field. As with other medical fields, there's too much of a tendency to use drugs to solve everything.
Got "social anxiety disorder?" (btw, most diagnoses of this are BS) No problem, Paxil to the rescue. Got a kid with ADHD? (btw, most diagnoses of THIS are also crap) Throw ritalin at him. Drugs should be the last option, and in many cases they're the first.