force
DESCRIPTION
FORCE. Chapter 10 Text. Force. A push or a pull in a certain direction SI Unit = Newton (N). Combining Forces. The combination of all forces acting on an object is the Net Force. When forces act in the SAME DIRECTION = ADDITION. When forces act in the OPPOSITE DIRECTION = SUBTRACTION. - PowerPoint PPT PresentationTRANSCRIPT
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FORCE
Chapter 10 Text
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Force•A push or a pull in a certain direction
•SI Unit = Newton (N)
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Combining Forces
•The combination of all forces acting on an object is the Net Force.
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•When forces act in the SAME DIRECTION = ADDITION
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•When forces act in the OPPOSITE DIRECTION = SUBTRACTION
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•Balanced Forces result in NO MOVEMENT
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= 0
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•Unbalanced forces
•cause a change in the object’s motion.
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Friction and Gravity
•Friction – the force that two surfaces exert on each other when they rub
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Types of Friction
•1. Static Friction•2. Sliding Friction•3. Rolling Friction•4. Fluid Friction
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Static Friction•Friction that acts on objects that are NOT moving
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Sliding Friction•Occurs when two surfaces slide over each other
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Rolling Friction•Occurs when an object rolls across a surface
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Fluid Friction•Occurs when solid objects moves through fluids such as water, oil, or air
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•Friction depends on two factors:
•1. How hard the surfaces push together
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•2. The type of surfaces involved
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Gravity•A force that pulls objects toward each other
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2 Factors Affecting Gravity
•1. Distance•2. Mass
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If Distance Increases the force of gravity Decreases
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Mass•The amount of matter in an object
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If mass increases, the force of gravity increases
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Mass vs. WeightMass is Constant because of the amount of matter does not change
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•The force of gravity on a person or object at the surface of a planet is known as weight.
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•Weight varies with the strength of the gravitational force, mass does not.
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Gravity and Motion
•Free fall – when the only force acting on a falling object is gravity
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•Acceleration due to gravity is
•9.8 m/s/s
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•All objects in free fall accelerate at the SAME rate regardless of their masses
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Why don’t objects fall at the same rate?
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Air Resistance•Falling objects with a greater surface area experience more air resistance.
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Terminal Velocity•Reached when the force of air resistance equals the weight of the object
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Newton’s Laws of Motion
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Newton’s 1st Law•an object at rest will remain at rest, an object in motion will stay in motion UNLESS acted upon by another force.
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Inertia
•Resistance to a change in motion
•Newton’s 1st Law
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•Inertia depends on mass, the greater the mass the greater the inertia
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Newton’s 2nd Law
•Force = mass x acc.
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•Acceleration =Net ForceMass
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End Unit for Acceleration
•kg•m/s/s•Kg•m/s2
•Newton
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• Textbook samples
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•Calculating: Calculate the slope of the graph. What does the slope tell you about the object’s motion?
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•The slope is 9.8. The speed increases by 9.8 m/s each second.
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–What will the speed of the object be at 6 seconds?
58.8 m/s
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•A speedboat pulls a 55-kg water-skier. The force causes the skier to accelerate at 2.0 m/s2. Calculate the force that causes this acceleration.
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•Fnet = m X a = 55 kg X 2.0 m/s2
• F = 110 kg • m/s2
• F = 110 N
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What is the net force on a 1,000-kg object
accelerating at 3 m/s2?
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Force = m x acc.
•(1,000 kg X 3 m/s2)•3,000 N
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•What net force is needed to accelerate a 25-kg cart at 14 m/s2?
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•Force = mass x acc. •(25 kg X 14 m/s2)•350 N
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Newton’s 3rd Law
•For every action there is an equal and opposite reaction
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Momentum
Momentum = Mass x Velocity
End Unit = kg m/s
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Conservation of Momentum•The total momentum of any group of objects remains the same, or is conserved, unless outside forces act on the objects
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•Which has more momentum: a 3.0-kg sledgehammer swung at 1.5 m/s or a 4.0-kg sledgehammer swung at 0.9 m/s?
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Momentum = Mass X Velocity
Smaller sledgehammer = 3.0 km X 1.5 m/s =
4.5 kg•m/sLarger sledgehammer = 4.0
km X 0.9 m/s = 3.6 kg•m/s
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•A golf ball travels at 16 m/s, while a baseball moves at 7 m/s. The mass of the golf ball is 0.045 kg and the mass of the baseball is 0.14 kg. Which has the greater momentum?
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• Golf ball: • 0.045 kg X 16 m/s =• 0.72 kg•m/s• Baseball: • 0.14 kg X 7 m/s = • 0.98 kg•m/s• The baseball has greater
momentum.
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•What is the momentum of a bird with a mass of 0.018 kg flying at 15 m/s?
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• (0.018 kg X 15 m/s =•0.27 kg•m/s
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Energy
Chapter 13
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Energy•The ability to do work
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•2 Kinds of Energy•1. Kinetic Energy•2. Potential Energy
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Kinetic Energy•Energy of MOTION
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•Kinetic energy increases as mass and velocity increases
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Potential Energy•Stored Energy
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Gravitational potential energy increases as weight and height increase.
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