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Published byKenneth Lambert Modified over 8 years ago
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Forces and Newton’s Laws of Motion
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Forces The natural state of an object –its behavior if free of external influences - is uniform motion with constant velocity. “At rest” has no special significance in Galileo’s view of motion. Influences that lead to deviations from uniform motion are called forces.
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Newton’s First Law of Motion Consider an object with no force acting on it. If it is at rest, it will remain at rest; If it is moving, it will continue to move in a straight line at constant speed. Consider the crash test dummy who continues in motion after the car has hit a wall. Always wear your seat belt! It’s just good physics!
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Properties of forces A force is a push or pull A force acts on an object. Forces do not act in isolation. A force requires an agent. An agent is something that pushes or pulls. It can be an inert object A force is a vector with magnitude and direction. The size or strength of the force is its magnitude.
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Properties of forces cont. A force can be either a contact force or a long range force. Contact forces are forces that act on an object by touching it at a point of contact (ex. Bat must hit ball to hit it) Long range forces are forces that act on an object without physical contact (ex. Gravity or a magnet)
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Forces In general the object exerts a force back on the agent. A force is really an interaction between two objects
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Drawing force vectors
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F N is the normal force. Normal means perpendicular. Include what is being acted on, by what. (object and agent) F g on the box by the earth FNFN
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More Force Drawings Forces can represent a push or pull. Either way they are depicted the same, acting on a particle
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Combining Forces The mathematical sumation is called the superposition of forces. The net force is the resultant. F NET is not a new force – The original forces are replaced by F NET.
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What is the net force?
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Net force
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Stop to Think Two of the three forces exerted on an object are shown. The net force points directly to the left. Which is the missing third force? CCCC
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Balanced Forces Forces are balanced if the object isForces are balanced if the object is Not moving orNot moving or At constant velocityAt constant velocity
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Unbalanced Forces Unbalanced Forces Forces are unbalanced if –The object starts moving –The object changes direction –The object stops If there is an unbalanced force an object will accelerate
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Inertia Inertia is an objects tendency to resist a change in motion Remember the crash test dummy
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