Newton's First Law of Motion tells us that objects at rest tend to stay at rest until acted upon by an outside force. In this case, the water is at rest in the bottle until the outside force (tilt) acts upon it. The water tends to want to stay at rest, and thus lags behind sloshing toward the opposite direction of the tilt. Like the water in the bottle, your ear has fluid-filled tubes, called semi-circular canals. As you move, the fluid in these tubes lags behind, and the nerves in your ear can feel this. This is sometimes referred to as "your sense of balance".

The student is able to communicate that the water sloshed in the opposite direction of the tilt due to Newton's First Law of Motion: objects at rest tend to remain at rest until acted upon by an outside force. The student is able to communicate that the water sloshed in the opposite direction of the tilt. The student is able to communicate that tilting the bottle caused the water to slosh in the bottle. The student is able to communicate that the water sloshed in the bottle.