Gravity can make a ball roll downhill without touching it. Kicking a ball can make it roll by touching it with a foot.To make something that is sitting still start moving, there always needs to be _______ on the object. A. light B. force C. heat D. contact

James gently releases a ball at the top of a slope, but does not push the ball. The ball rolls down the slope. Which force caused the ball to move downhill? A. applied force B. drag force C. friction force D. gravitational force E. normal force

Hannah’s class plays kickball at recess. The ball is rolling toward Hannah. She kicks the ball. It moves in the opposite direction. Which type of force caused the ball to change direction? A. gravity B. friction C. pull D. push

Let us first guess the answer based on our commonexperience. To move a football at rest, someone must kick it.To throw a stone upwards, one has to give it an upwardpush. A breeze causes the branches of a tree to swing; astrong wind can even move heavy objects. A boat moves in aflowing river without anyone rowing it. Clearly, some externalagency is needed to provide force to move a body from rest.Likewise, an external force is needed also to retard or stopmotion. You can stop a ball rolling down an inclined plane byapplying a force against the direction of its motion.In these examples, the external agency of force (hands,wind, stream, etc) is in contact with the object. This is notalways necessary. A stone released from the top of a buildingaccelerates downward due to the gravitational pull of theearth. A bar magnet can attract an iron nail from a distance.This shows that external agencies (e.g. gravitational andmagnetic forces ) can exert force on a body even from adistance

8Jeremy throws his ball up in the air, but the ball falls back to the ground. What force made the ball move without ever touching the ball? A. the air pressure pushing on the ball B. magnetism pulling on the ball C. Jeremy's hand pushing on the ball D. gravity pulling on the ball

A golf ball is on a tee. It is hit with a golf club. The ball flies through the air. Which type of force caused the motion of the ball? A. friction B. push C. pull D. gravityReset