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# Download FORCES - Mr. Maloney

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FORCES episode II newton strikes back Physics Mr. Maloney A new era of physics Aristotle (384-322 BC) thought that objects were naturally at rest, would always stop themselves and a force was needed for any motion. Descartes (1596-1650) thought that some unseen vortex was constantly pushing on things to make them stay in motion. Galileo (1564-1642) realized that the Greeks weren't accounting for forces such as friction. Newton summarized Galileo's thoughts and others through his three laws of motion. © 2002 Mike Maloney objectives You will be able to describe how mass, force and acceleration are related to eachother. describe the consequences of Newton’s 2nd Law. graph data to find a relationship between variables. Jump to Post Lab © 2002 Mike Maloney Newton’s 2nd Law Newton’s 2nd law describes how a mass behaves when forces act on it. We can guess these forces will produce a change in motion but how are they related? ILD 2.2 (1st part) © 2002 Mike Maloney Newton’s 2nd Law How does acceleration relate to force? Lets do a little experiment together as a class to find out. Force Sensor Accelerometer © 2002 Mike Maloney Newton’s 2nd Law How does this acceleration relate to the force? The acceleration will be in the same direction as the force. The magnitude of the acceleration increases as the force increases The magnitude of the acceleration decreases as the mass of the object increases Recreate our lab using this sim. © 2002 Mike Maloney N2L with multiple objects What if there is more than one object applying a force on some mass? What is the effect now? (back to ILD) It is not just one force that determines how an object will change it motion, it is the sum total of all forces acting on the object … what we call NET FORCE. Demos with 2 fans and 2 weights. © 2002 Mike Maloney Newton’s 2nd Law In mathematical terms a = F/m acceleration = net force / mass or more commonly written Force (net) = mass ∙ acceleration F = m∙a And since force and acceleration are vectors, they will be in the same direction. © 2002 Mike Maloney MEASURING FORCES The unit of force is the Newton {N} It is derived from its effect. F = m*a [kg]*[m/s2] 1 N = 1 kg•m/s2 1 N is defined as the amount of force required to accelerate 1 kg at a rate of 1 m/s2. © 2002 Mike Maloney 2nd Law Examples Accelerating a car vs. truck Slowing down a car vs. truck Jogging vs. sprinting Pushing chair alone vs. someone in it Freefall © 2002 Mike Maloney objectives Can you describe how mass, force and acceleration are related to eachother. describe the consequences of Newton’s 2nd Law. graph data to find a relationship between variables. Jump to Post Lab © 2002 Mike Maloney APPENDIX © 2002 Mike Maloney Inertia The tendency of an object to resist a change in motion is called its inertia. Objects with greater masses generally have greater inertias. For our purposes, an object’s inertia is basically measured by it mass. BACK © 2002 Mike Maloney Net Force NET FORCE refers to the vector sum total of all forces acting on an object. It is often expressed as F For example, if there were two leftward forces of 10 lb each, the NET FORCE would be 20 lb leftward. If there were one 10 lb rightward force and one 8 lb leftward force, the NET FORCE would be 2 lb rightward. What about if the forces were in X and Y? BACK © 2002 Mike Maloney Applied Force APPLIED FORCE refers to a generic force that is acting on an object. An APPLIED FORCE is basically any force that is not a WEIGHT, NORMAL FORCE, FRICTIONAL FORCE, SPRING FORCE, or other named force. BACK © 2002 Mike Maloney