Study Guide: Chapter 9- Measuring Motion 1. How do you know you are moving? motion: an object is in motion if its distance from another object is changing. reference point: a place or object used for comparison to determine if something is in motion. a. For example, imagine you are on a train sitting in a seat next to your best friend. The train is going 70 mph. If you use your friend as the reference point, it would appear that you are not moving. BUT if you use the tree outside as a reference point it would appear that you are moving 70 mph. 2. What is speed? a. If you know the distance an object travels in a certain amount of time, you can calculate the speed of the object. BECAUSE…the speed of an object is the distance the object travels per unit of time. b. The speed of most objects is not constant, and therefore, the average speed is often used in place of the instantaneous speed (the actual speed at that instant – like the speed measurements that police officers make with “radar guns”). Average speed = final distance – initial distance Time What is velocity? The direction and speed an object travels. 4. What is acceleration? The rate at which velocity changes by way of increasing speed, decreasing speed, or changing direction. 5. How can we know if an object is accelerating? Acceleration = Final speed – Initial speed Time Chapter 10 - Force 1. What is force? A push or pull 2 2. What is the difference between a balanced and an unbalanced ) force? Balanced forces – object does not move Unbalanced forces change the velocity of an object and cause an object at rest to move. Forces Acting in Same Direction 5N + 10 N Net Force: 15 N (unbalanced) Forces Acting in Opposite Directions 5N + 10 N Net Force: 5 N (unbalanced) 5N 5N Net Force: 0 N (balanced) 7. What are Newton’s Laws of Motion? 3. Describe two examples of force. Gravity and Friction Newton's First Law An object's motion can only be changed by unbalanced Friction is a contact force. forces. The law of universal gravitation states that all objects are attracted to According to Newton's 1st Law, the motion of an object is each other by gravity. not changed by balanced forces acting on it. Friction can stop or slow down objects sliding past each other. Inertia is the tendency of an object to resist its change in Friction acts in the opposite motion of the object. motion There are 4 different kinds of friction. Newton's Second Law Terminal velocity and free fall According to Newton's 2nd Law, an objects acceleration is 4. Is friction useful or not? the net force on the object divided by its mass. In circular motion, a centripetal force pulls an object Helps us walk and stop our car toward the center of the curve. Formula Force = mass x acceleration Newton's Third Law 5. What is the difference between mass and weight? Mass is the amount of matter and weight is the measure of gravitational force 6. What factors affect gravity and friction? Friction depends on type of surface. Gravity depends on distance and mass. Newton's 3rd Law states that when one object applies a force on another, the second object applied an equal force in the opposite direction on the first object. The forces of a force pair do not cancel because they are acting on different objects. According to the law of conservation of momentum, momentum is conserved during a collision unless an outside force acts on the colliding objects. Formula Momentum = mass x velocity