Catapults are designed to provide a 'push' which will be stronger than the force of gravity - the object which is being catapulted should be aerodynamic to minimize which force?

There are many types of force, such as thrust, magnetism and gravity. Different forces which act on objects.  Friction (which slows things down), gravity (which pulls things towards the Earth or other large body), magnetism (which attracts certain metals and repels opposite magnetic poles), air resistance and water resistance (which both drag on moving objects) - these are all different types of pushes and pulls.