__ forces always cause on object's motion to change. contact unbalanced non-contact balanced

## Step 1<br />The problem is asking us to identify the type of force that always causes a change in an object's motion. The options provided are contact, unbalanced, non-contact, and balanced forces.<br /><br />## Step 2<br />Let's analyze each option:<br />- Contact forces are those that require physical contact between the objects involved. They can be balanced or unbalanced.<br />- Non-contact forces are those that do not require physical contact between the objects involved. They can also be balanced or unbalanced.<br />- Balanced forces are those that are equal in magnitude and opposite in direction, resulting in no change in motion.<br />- Unbalanced forces are those that are not equal in magnitude and/or not opposite in direction, resulting in a change in motion.<br /><br />## Step 3<br />From the above analysis, it is clear that unbalanced forces are the ones that always cause a change in an object's motion.