Force A. Force is the __ of acceleration, or change in an object's velocity. 1. The combination of all the forces acting on an object is called the __ 2. __ completely cancel each other and equal zero. 3. __ do not cancel each other out and do not equal zero. III. Friction and Air Resistance A. __ is the force between two objects in contact that opposes the motion of either object. 1. Vary depending on the __ 2. __ is a form of friction. a. Depends on __ and __ as well as the __ in which it moves. IV. Gravity A. Gravity is the __ between two objects due to their __ 1. __ and __ affect gravitational force.

Force<br />A. Force is the **cause** of acceleration, or change in an object's velocity.<br />1. The combination of all the forces acting on an object is called the **net force**.<br />2. **Balanced forces** completely cancel each other and equal zero.<br />3. **Unbalanced forces** do not cancel each other out and do not equal zero.<br /><br />III. Friction and Air Resistance<br />A. **Friction** is the force between two objects in contact that opposes the motion of either object.<br />1. Vary depending on the **surfaces in contact**. (e.g., roughness, materials)<br />2. **Air resistance** is a form of friction.<br /> a. Depends on **speed** and **surface area**, as well as the **shape** in which it moves.<br /><br />IV. Gravity<br />A. Gravity is the **force of attraction** between two objects due to their **masses**.<br />1. **Mass** and **distance** affect gravitational force.<br />