Answer:

When pushing a object it doesn't move immediately due to its mass.

Or more specifically the gravity pulling on its mass. This causes friction which counters the force of the push. The only way the object will move is when the pushing force exceeds the friction force. When's starts moving it basically accelerating from 0 to an arbitrary speed.

So the heavier an object the harder you need to push .

But if you use the same amount force on a lighter object, it cross a larger distance then the lighter object in the same amount of time. Crossing a larger distance in the same amount of time means the lighter object moved faster. And that means the lighter object reached the heavier one's top speed faster. And that means it accelerated faster.

In short the lighter an object the faster it accelerates or the heavier an object the slower it accelerates

Explanation:

Here's an easy example for you ;

Imagine pushing a fat guy as hard as you can and then imagine pushing with the same force a thin guy, you would see that the thin guy would just fly off, whereas the fat one would have hardly moved.

Mass is just resistance to acceleration, the more mass an object has the harder it is to increase its speed in other words you have to put more force to accelerate it.

Scientifically said: the mass is inversely proportional to the acceleration