भौतिकशास्त्रानुसार बल अथवा प्रेरक म्हणजे एखाद्या पदार्थाची गती बदलण्यास पुरेसे वास्तविक कारण होय.
Something or anything that has the power to produce a physical effect upon something else, such as causing it to move or change shape.