Download - PATTERNS OF MOTION AND EQUILIBRIUM
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PATTERNS OF MOTION AND EQUILIBRIUM
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Galileo`s concept of inertia • Force: is a push or pull. It is
needed to start an object moving. No force is needed when it starts moving, just the force to overcome friction.
• Inertia: the property of things to resist changes in motion. So a ball moving horizontally would move forever if friction is totally absent.
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Concept of inertia
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Concept of inertia • Every material object
possesses inertia: how much depends on its amount of matter. The much matter, the much inertia (that means it has more mass)
• When comparing 2 objects, you should compare the abilities to be resistant to a change in motion.
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Mass vs Weight • Mass: quatity of matter in an
object. It`s a measure of inertia that an object exhibits in response to any effort made to start it, stop it, or change its state of motion in any way. (SI Unit: Kilogram)
• Weight: force upon an object due to gravity. (SI Unit: Newton) W=m x g
• Directly proportional to each other. • Gravitation force: 9.8N• 1 Kg= 9.8N
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Vectors and scalars• Vector quantity: directed
quantity. It has to be specified not only by magnitude (size) but by direction as well. May be represented by arrows Ex: velocity
• Scalar quantity: can be specified by magnitude alone. Ex: speed
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Adding vectors
• Vectors that are add together are called component vectors. The sum of component vectors are called a resultant.
• DO NOT MIX VECTORS!!!!!
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Net force• Objects don`t speed up, slow down or change
direction unless a force acts.• The NET FORCE is the total force acting on an
object. A combination of forces that changes an object`s state of motion.
• It is a vector quantity, arrows represented the direction of the quantity.
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The equilibrium rule
• Forces are balanced
• There`s no motion
• Called mechanical equilibrium
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Support force
• Called NORMAL force
• The force that supports an object against gravity
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Dynamic equilibrium
• STATIC equilibrium: when an object is NOT moving
• DYNAMIC equilibrium: once in motion, if there is no net force to change the state of motion, it moves at an unchanging speed.
∑F= 0
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Force of friction• Resistive force that opposes the motion or
attempted motion of an object past another with which it is in contact.
• For solids, liquids and gases
• ALWAYS in opposite direction to motion
• Ex: air resistance
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Force of friction
• Depends on: the kind of material and how much surfaces are pressed together
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Types of Friction
• Dry friction:
- Static friction: the object has no motion.
- Sliding friction: the object moves.
• Lubricated friction: Needs a lubricant to start moving.
• Fluid friction: resistance in liquids.
• Air resistance: resistance of an object to move in the air.
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Instantaneous speed
• The speed at any instant
• Most of the time, it is different than the average speed
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Velocity• Constant velocity means constant speed and
direction• Direction in a straight line: no curves• No change in velocity, means no acceleration• Works with displacement (net distance)
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Motion is relative
• Everything is always moving
• Motion is relative to different objects
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Acceleration• Variation is motion, in velocity
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Average acceleration
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Acceleration• Recognizing Acceleration on a Graph
Acceleration can be shown on a graph of velocity versus time.
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Tracks• Circular Motion: Continuous Acceleration
An object traveling in a circular motion is always changing its direction. Therefore, its velocity is always changing, so it is accelerating.
• The acceleration that occurs in circular motion is known as centripetal acceleration.
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Tracks
• Linear motion: motion along a straight line.
• It can be uniform, with constant speed or non uniform with a variable speed
• An example of linear motion is that of a ball thrown straight up and falling back straight down.
• objects not subjected to forces will continue to move uniformly in a straight line indefinitely
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Tracks
• Parabolic motion: A projectile is an object upon which the only force is gravity. Gravity, being a downward force, causes a projectile to accelerate in the downward direction.