The "transit method" means doing very careful precise measurements as the planet passes in front of its star.
It's too far away for us to see it directly, but when it "transits" the star, the brightness of the star decreases by a tiny tiny tiny bit, which we can measure.
If we can measure that dip with good enough precision, it tells us how much of the star's photosphere was blocked from our view when the planet temporarily got in the way. From that, we can estimate the planet's <em>size</em>.
If there is a net force acting on an object, the object will have an acceleration and the object's velocity will change. ... Newton's second law states that for a particular force, the acceleration of an object is proportional to the net force and inversely proportional to the mass of the object.
