Tables and floors can also support the bag of apples, stopping the bag falling. If you drop the bag, that stopping might be rather sudden, damaging the apples. The floor or a wall can also change how something is moving: a ball bounces off a wall or a floor.
Just like you
exert a force on a bag, so the table can
exert a force on the bag. It's not only you. Many other things can push and pull, exerting forces. Fortunately, there are only a few kinds of forces, which you can learn to identify. Spotting these patterns makes thinking with forces easier.
Forces are always exerted by you or another agent, and acting on something. That's because the idea of a force is a simple way of talking about the many small-scale happenings when you support a bag or catch a ball. Focus on the thing and the force acting on the thing, leaving out what's exerting the force to draw this simply.
Physics shows the world simply.
There are nine kinds of forces in three groups. Each of the three groups acts on things in different ways, so draw the forces in different ways.
Support forces act on top or bottom surface, at right angles to the surface. Frictional forces act on a surface, always related to moving or not moving; non-contact forces act on the centre.
Change environments, and you change what's there to exert a force. There are nine kinds of exerting to look for, so nine kinds of forces.
Read on to learn to identify each kind of force.