Transcript force
What is a Force? FORCE = Any push or pull which causes something to move or change its speed or direction What is a Force? Forces can be BALANCED or UNBALANCED Balanced forces are equal in size and opposite in direction UnBalanced forces are not equal in size and/or opposite in direction. If the forces on an object are UNBALANCED, we say a NET force results. What is a Force? Can you think of examples of forces? Balanced Forces? Unbalanced Forces? Force I. Force A. a push or pull that one body exerts on another B. What forces are being exerted on the football? Fkick Fgrav Measuring Forces I. I. Forces are measured in newtons (kg . m/s2). Forces are measured using a spring scale. Force I. Balanced Forces A. forces acting on an object that are opposite in direction and equal in size B. no change in velocity Force I. Net Force A. unbalanced forces that are not opposite and equal B. velocity changes (object accelerates) Fnet Ffriction Fpull N N W ConcepTest 2 You are a passenger in a car and not wearing your seat belt. Without increasing or decreasing its speed, the car makes a sharp left turn, and you find yourself colliding with the right-hand door. Which is the correct analysis of the situation? ... ConcepTest 2 1. Before and after the collision, there is a rightward force pushing you into the door. 2. Starting at the time of collision, the door exerts exerts aa leftward leftward force force on on you. you. door 3. both of the above 4. neither of the above ConcepTest 1 TRUE or FALSE? The object shown in the diagram must be at rest since there is no net force acting on it. FALSE! A net force does not cause motion. A net force causes a change in motion, or acceleration. Taken from “The Physics Classroom” © Tom Henderson, 1996-2001. What is Gravity? GRAVITY: An attraction force between all masses Newton’s universal law of gravitation: Every object in the universe exerts a gravitational attraction to all other objects in the universe The amount of gravitational force depends upon the mass of the objects and the distance between the objects What is Gravity? The greater the mass, the greater the force The greater the distance, the less the force Acceleration due to gravity = 9.8 m/s/s or 9.8 m/s2 Gravity A.force of attraction between any two objects in the universe B.increases as... 1.mass increases 2.distance decreases Gravity I.Who experiences more gravity - the astronaut or the politician? I.Which exerts more gravity the Earth or the moon? less distance more mass Gravity I.Would you weigh more on Earth or Jupiter? A.Jupiter because... greater mass greater gravity greater weight What is Motion? Motion: A change in position of an object compared to a reference point What is Friction? Friction = A force that opposes or slows down motion Caused by the physical contact between moving surfaces The amount of friction depends upon the kinds of surfaces and the force pressing the surfaces together Changes motion into heat Friction A. force that opposes motion between 2 surfaces B. depends on the: 1. types of surfaces 2. force between the surfaces I. Friction Four Types of Friction Static Friction – force that acts on objects that are not moving. (Couch Potato) Sliding Friction - force that opposes the direction of motion of an object as it slides over a surface. (Ice skating or bobsledding) Rolling Friction – friction force that acts on rolling objects. (Rollerblading) Fluid Friction – force that opposes the motion of an object through a fluid. (Planes flying or submarines traveling)