Name the physical quantity which causes motion in a body.

Explanation

**Step-by-Step Solution:**

1. **Understanding Motion**: Motion refers to the change in position of an object with respect to time. For an object to be in motion, it must experience a change in its state of rest or uniform motion.

2. **Identifying the Cause of Motion**: To determine what causes motion, we need to consider the factors that can change the state of an object. This includes any influence that can make an object start moving, stop moving, or change its direction of motion.

3. **Defining Force**: The physical quantity that is responsible for causing motion in a body is known as "force." Force is defined as any interaction that, when unopposed, will change the motion of an object.

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