1. Force of Gravity: This is the force that attracts objects with mass towards each other. On Earth, gravity pulls objects towards the center of the planet, causing them to accelerate downwards. This affects both the speed and direction of an object's velocity. For example, a ball thrown upwards will slow down as gravity pulls it back down, eventually changing its direction to fall towards the ground.

2. Friction: This force opposes the motion of an object when it comes into contact with a surface. Friction can cause an object to slow down or even stop. There are different types of friction, including:

* Static Friction: The force that prevents an object from starting to move.

* Kinetic Friction: The force that acts on an object that is already moving.

Here's how friction affects velocity:

* Decreasing speed: Friction causes a moving object to lose energy and slow down. Think of a car braking or a ball rolling to a stop.

* Changing direction: Friction can also change an object's direction. Imagine a car skidding on a slippery road - friction with the road causes the car to slide sideways.

These are just two examples, and there are many other forces that can affect an object's velocity, such as:

* Applied force: This is a force that is directly applied to an object, like pushing a box or pulling a rope.

* Normal force: This is the force that a surface exerts on an object that is in contact with it, like a table supporting a book.

Understanding forces is key to understanding how objects move in the world around us!