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An object in motion tends to stay in motion. The ketchup is an extremely viscous fluid. If the bottle is inverted, gravity induces a force on the mass of ketchup. That force is the acceleration of gavity times the mass of the ketchup. The pull of gravity, however, is insufficient to dislodge the ketchup which is held in place by negative pressure between the bottom of the bottle and the mass of ketchup. The viscosity of the ketchup does not allow air to pass through the ketchup mass and occupy the space at the bottom of the bottle that is currently occupied by ketchup. In order to move the mass of viscous fluid, additional force is needed. Acclerate the bottle downward and then rapidly decelerate the bottle. The relative force is (acceleration of gravity plus deceleration of bottle) times mass of ketchup. If you are fast enough, some of the viscous mass will slip in relation to the rest of the viscous mass and come out of the bottom of the bottle. The displaced volume will be replaced by air, and you will have to repeat the procedure to extract more ketchup. Be careful! Once an unobstructed air channel is established from outside of the bottle to the bottom of the bottle behind the ketchup mass, there will no longer be negative pressures to hold the ketchup in place. This can lead to the entire contents of a bottle of ketchup smothering a standard serving of curly fries.

1. Ketchup experience acceleration, like you in a car.

2. Bottle is abruptly halted, like you slamming on the brakes.

3. Ketchup experiences similar motion due to inertia, like you flying forward after slamming on the brakes.

the 1st law of motion is inertia