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Lesson One‐Newton’s First Law Name_______________________________ Source: http://www.physicsclassroom.com/Physics‐Tutorial/Newton‐s‐Laws Section A Newton’s First Law 1. State Newton’s First Law: An object at rest stays at rest and an object in motion continues to move at the same speed and in same direction unless acted upon by an unbalanced force. 2. The state of motion of an object is maintained as long as the object is not acted upon by an _____unbalanced force__________ 3. All objects resist ____a change in its motion__________ ‐ they tend to "keep on doing what they're doing." 4. What device in an automobile provides an unbalanced force that brings you from a state of motion to a state of rest?____brakes___________ How does this device accomplish this? Force of the brake pads on the rotor of the wheel causes the wheel to be slowed. This friction reduces the speed of the car 5. How would Newton’s First Law apply to blood rushing from your head to your feet while quickly stopping a descending elevator? Since force is applied externally it has no effect on blood. Blood continues moving in a downward direction until it can no longer do so. 6. How would Newton’s First Law apply to your falling forward when you trip over a rock? When tripping over a rock, your foot has the force applied to it causing it to stop. Your upper body does not experience the force and continues to move forward. Section B Inertia and Mass 7. Define inertia : The resistance an object has to its state of motion 8. The idea that dominated people's thinking for nearly 2000 years prior to Newton was that it was the natural tendency of all objects to assume a rest position. Explain this statement. Ancient peoples believed that the natural state of all objects was at rest. They believed that a force was needed to maintain motion. Newton suggested his First Law which disputed that claim 9. Who developed the concept of inertia?___Galileo_________ 10. Sketch and explain Galileo’s experiment illustrating the concept of inertia. Without friction ball would rise to the same height. In experiment, friction prevented ball from rising to the exact same height. If flat and without friction, ball would roll forever‐move inertially 1. A force (is, is not) required to keep a moving object in motion. 12. All objects resist changes in their state of motion. All objects have inertia. The more inertia that an object has, the (more massive it is, less massive it is,...mass does not affect inertia) 13. Without lifting them, how could you tell the difference between a concrete brick and a styrofoam brick that appear to be identical? Apply equal force to the two objects, the object moved more easily would have less inertia and, therefore, less mass. 14. Read Check Your Understanding and be able to discuss the correct answers. 1. Rock would continue forever unless acted upon by an unbalanced force 2. No force is needed for there is no acceleration 3. Inertia is independent of speed Section C State of Motion 15. How could you redefine inertia utilizing the term velocity? Tendency of an object to resist a change in its velocity 16. How could you redefine inertia utilizing the term acceleration? Tendency of an object to resist acceleration Section D Balanced and Unbalanced Forces 17. How would you describe balanced forces? When all forces acting on an object in one direction are opposed by equal forces in the opposite direction. The sum of all forces in one direction adds to zero...zero net force 18. When forces are balanced , they are said to be in ____equilibrium_______ 19. If an object is not at equilibrium and subsequently accelerates, what is the cause of the acceleration? ________the unbalanced forces____________ 20. Balanced forces must be _____equal in size_______________and __________________ _____opposite in direction_____. 21. If the term net force refers to the adding up of all forces acting in one direction. The net force resulting from balanced forces would be (equal to zero, less than zero, greater than zero) The net force resulting from unbalanced forces would be (equal to zero, not equal to zero)