I will assume you refer to the initial acceleration when you speak of "while on takeoff", since after the rotation the answer would be quite tautological.
Let's be clear, the nose gear does not "extend" anywhere during take-off since its damper/shock absorber is not an active component, but rather a passive one.
The effect you are feeling is due to the acceleration and the inertia of the aircraft: the engines of a large aircraft sit below the Center of Mass which will incur a rotational force to the aircraft, lifting the nose up a bit. The weight will be "sitting" more on the main gear rather than the nose, you have a similar effect on a car or, more notably, on an accelerating motorcycle.
You also have the reverse effect when decelerating: the weight will tend to stress more the nose gear rather than the main gear, the same way a motorcycle tends to "sit" on the front wheel when stopping.
On aircraft with the engines up high the rotational force will be reversed until the elevators have enough airflow to counteract it.