Halley's comet does not always get less velocity. Its velocity changes throughout its orbit, and it actually speeds up as it approaches the Sun and slows down as it moves away from the Sun.

Here's why:

* Gravity: The Sun's gravity is the main force affecting Halley's comet's velocity. As the comet gets closer to the Sun, the gravitational pull becomes stronger, causing the comet to accelerate. This is similar to how a ball thrown upwards slows down as it goes against gravity, but speeds up when falling back down.

* Orbital mechanics: Halley's comet follows an elliptical orbit around the Sun. At its closest point (perihelion), it moves fastest, and at its farthest point (aphelion), it moves slowest. This is due to the conservation of energy and angular momentum in the comet's orbit.

Therefore, it's not accurate to say that Halley's comet always gets less velocity. Its velocity changes constantly throughout its orbit, and it speeds up when approaching the Sun and slows down when moving away.