Describe the balanced forces acting on an object moving at a constant speed along a straight line, 1st Law of Motion (e.g., a car traveling at a constant speed of 60 mph on a straight freeway has a force pushing it forward balanced by frictional forces acting in the opposite direction). Explain how unbalanced forces change the speed and/or direction of motion of different objects moving along a straight line, 2nd Law of Motion (e.g., a 2-kg object needs twice the unbalanced force to speed up the same amount as a 1-kg object). Investigate and describe that forces always come in pairs, 3rd Law of Motion (e.g., pull a spring scale against another spring scale, as water blasts out of a bottle rocket two forces act - a force on the water and an equal force on the rocket).