Force and Motion

Gravity is a force that pulls objects toward the center of the larger mass (which is always Earth since we are always on this planet). All matter (anything that has mass and takes up space) has gravity though- a pencil, a piece of bread, a paper clip...... we just don't feel the effects of gravity on these smaller objects (and our own gravitational pull) because the Earth's pull is SO much stronger than everything else.

A force is a push or a pull. A force can give energy to an object causing the object to start moving, stop moving, or change its motion. Forces occur in pairs and can be either balanced or unbalanced.  
Some examples of forces are gravity, friction, air resistance, and magnetism

Balanced forces do not cause a change in motion. They are equal in size and opposite in direction
In our lab on changing a marble's speed, we learned that gravity is one of the forces acting on the marble, which is why it rolled down our ruler ramps when we released it for each of our trials. We also learned that friction was another force acting on the marble, which helped the marble slow down and eventually come to a complete stop after it rolled down the ramp and across the floor. Once the marble came to a complete stop, the forces on the marble were balanced (and there was no longer a change in the marble's motion).
Forces were UNBALANCED while the marble was rolling down the ramp and across the floor. Any time there is movement with an object, forces are not balanced.

In this Tug of War example, forces are NOT balanced. The group on the left is pulling with more force than the group on the right (the group is moving in the direction of the greater force).

In this Tug of War example, if both groups of people are pulling in opposite directions with the same amount of force, the rope will NOT move and forces will be balanced.

If two forces are working in opposite directions (against each other as in the Tug of War example), we subtract them. If we could measure the force that the left group is using to pull the rope in their direction and that the right group is using to pull the ropes in the opposite direction, we could subtract those forces to find the NET FORCE.

In contrast, if two force are working together in the same direction, we add them together. Person 1 + person 2 + person 3 (all on the left) are working together to pull back to the left. If we add their individual pulling forces together, we would get their combined total force.

Click here to review balanced and unbalanced forces: Quiz Yourself 

For Behavior Bucks, leave a comment offering two new examples- one for BALANCED forces and one for UNBALANCED forces.