Activity 79 Analysis Questions Describe the changes in direction and speed of the marble when they’re inside the circular track? The marbles’ direction changed constantly inside the circular track because of the force the wall exerted on the marble. Similarly, the surface of the circular track rubbed on the marble and slowed in down slightly. outside of the circular track? The direction once outside the circular track was in a straight line, moving across the table as shown on Transparency 79.1, “Inertia Diagrams”. The speed slowed slightly because of the table surface rubbing on the marble.

Describe any changes in the path of the marble that occurred when you changed the opening position of the circular track. The marble left the opening in a different direction for each opening position. Once it left the circular track, however, it continued in a straight line. mass of the marble. When comparing the glass (lighter) marble to the heavier (metal) one, no changes occurred to the direction that the marble traveled.

Imagine that a car is approaching a curve in the road when it suddenly loses its steering and brakes. The area is flat and there is no guardrail on the road. Copy the diagram below in your science notebook. Then draw a line showing the car’s path when it loses its steering and brakes.

Explain why the car will take that path. Because of inertia, which in the absence of other forces keeps moving objects moving in a straight line. How would your answer change if the car had more mass? Explain. More mass will not change the direction the car travels. It would, however, affect the force needed to stop the car.

Activity 79 Major Concepts An object that is not being subject to a force will continue to move at a constant speed in a straight line.

On your next blank page, take notes Force Notes

Net Force In many situations, including driving, more than one force is acting on an object. The combination of all forces acting on an object is the net force. Net force determines whether, and by how much, an object’s motion is changed. Total Force

Force Diagrams Objects are shown as a rectangle or square.

Force Diagrams A push or pull (force) is shown with an arrow

Force Diagrams The arrow always points AWAY from the object.

Force Diagrams The bigger the force, the bigger the arrow

Force Diagrams Label the arrows with the magnitude (amount) of the force (in N) 3 N 10 N

Force Diagrams Net Force is the sum of all of the forces 3 N 10 N 7 N

Practice: Draw an object with two forces acting in opposite directions with one force equal to 2 N and one force equal to 8 N.

Force Diagrams 2 N 8 N

Net Force Draw the net force acting on this object. 2 N 8 N

Force Diagrams Net Force 6 N

Balanced vs. Unbalanced Forces If there is a situation of unbalanced forces, there is a net force. Balanced forces mean there is a net force of zero on the object. Describe the motion of the blocks below. 2 N 10 N A. 8 N 8 N B.