Answer the following question given this paragraph: 

Consider the ramp in Figure below . It’s easier to push the heavy piece of furniture up the ramp to the truck than to lift it straight up off the ground. However, pushing the furniture over the surface of the ramp creates a lot of friction. Some of the force applied to moving the furniture must be used to overcome the friction. It would be more efficient to use a dolly on wheels to roll the furniture up the ramp. That’s because rolling friction is much less than sliding friction. As a result, the efficiency of the ramp would be greater with a dolly.


Q: What does pushing an object over the surface of a ramp cause?


A:
friction