G-Force
The g-force of an object is its acceleration relative to free fall. On earth this is 1g, or 9.8 meters per second squared (m/s^2) or equivalently  newtons of force per kilogram of mass (N/kg). Astronauts experience unusually high and low g-forces. G-force can also be seen on rollercoasters. When the coaster goes down the drop, you are pushed back into your seat because of g-force. Negative g-forces is when gravity is pushing you downwards causing you to feel weightless. (Going down a rollercoaster) Positive g-forces is when gravity is pushing against you causing you to feel heavier. (Going up a rollercoaster)