ch. 2 the laws of motion · 2016. 9. 21. · balanced forces - forces acting on an object ......
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Ch. 2 The Laws of Motion
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Lesson 1 Gravity and Friction
Force - A push or pull
we pull on a locker handle push a soccer ball or on the computer keys
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Contact force - push or pull on one object by another that is touching it.
Noncontact force - a force that one object can apply to another object without touching it
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Some contact sports?
Noncontact sports?
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Forces have both strength and direction. can be shown by arrows
The SI unit of force is the Newton (N)
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Gravity - an attractive force that exists between all objects that have mass.
Mass - the amount of matter in an object
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The law of universal gravitation states that1. All objects are attracted to each other by
a gravitational force.2. The strength of the force depends on the
mass of each object and the distance between them.
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As mass increases, gravitational forces increase
As distance increases, gravitational forces decrease
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Weight - the gravitational force exerted on an object
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Friction - a force that resists the motion of two surfaces that are touching
there are several types:
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Static Friction - friction between two objects that are not movingSliding Friction - friction between two objects that are sliding past each otherFluid Friction - friction between a surface and a fluid (liquid or gas) in air - air resistance
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Causes of friction - - roughness of the surfaces - weak electrical charges between atoms and molecules
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How can friction be reduced? - reduce the contact area between the microscopic bumps on the surface - reducing the surface area (air resistance)
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Lesson 2 Newton’s First Law
Review Forces - a push or pull
Net Force - the combination of all the forces acting on an object need reference direction
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Balanced Forces - forces acting on an object that combine and form a net force of zero
Unbalanced Forces - forces acting on an object that combine and form a net force that is not zero
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Newton’s First Law of Motion Every object continues in a state of rest or of uniform speed in a straight line unless acted on by a nonzero net force.
If the net force on an object is zero, the motion of the object does not change.
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Inertia - the tendency of an object to resist a change in its motion
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Lesson 3 Newton’s Second Law
Forces change an object’s motion Only unbalanced forces change an object’s velocity
Change in velocity means a change in speed, or direction or both.
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Velocity (from last chapter) is speed and direction of an object.
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Acceleration is the change in velocity over time.
Unbalanced forces can make an object accelerate by changing its speed, its direction, or both.
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Newton’s Second Law
The acceleration of an object is equal to the net force acting on the object divided by the object’s mass.
a = F/m
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Circular Motion - any motion in which an object is moving along a curved path
Centripetal Force - in circular motion, a force that acts perpendicular to the direction of motion, toward the center of the curve
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Lesson 4 Newton’s 3rd Law
The 3rd law states: when one object exerts a force on a second object, the second object exerts an equal force in the opposite direction on the first object.
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Force Pair - the forces two objects apply to each other
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Momentum is the measure of how hard it is to stop a moving object.
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The Law of Conservation of Momentum The total momentum of a group of objects stays the same unless outside forces act on the objects.
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Momentum Equation momentum = mass x velocity p = m x v
or v = p/m or m = p/v
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momentum before collision = momentum after collision
momentum of 2 cars momentum of bothbefore collision = cars after collision
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Elastic Collision - objects bounce off each other
Inelastic Collision - objects stick together
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A ball with a momentum of 16 kg m/s strikes a ball at rest. What is the total momentum of both balls after the collision?
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first ball p = 16 kg m/ssecond ball at rest p = 0
total of both before impact p = 16 kg m/s
since momentum is conserved - same after collision as before, after collision has to be 16 kg m/s also.
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The force of a bat on a ball and the force of a ball on a bat are _____ _____.
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A 2.0 kg ball rolls to the right at 3.0 m/s.A 4.0 kg ball rolls to the left at 2.0 m/s. What is the momentum of the system after a head on collision of the two balls?
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Reference direction - to the right
Total momentum before collision:(2.0 kg)(3.0 m/s) + (4.0 kg)(-2.0m/s) 6.0 + -8.0 = -2 kg m/s
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What is Newton’s 1st Law of Motion?
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An object at rest remains at rest, or an object in motion remains in motion, in a straight line, unless an unbalanced force acts on it.
What is inertia?
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The tendency of an object to resist a change in motion.
What force resists motion?
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Friction
The gravitational force exerted on an object is its weight or mass?
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Weight.
What is mass?
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The amount of matter in an object
The strength of gravitational force depends on ________ and ___________
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mass of the objects and distance between them
What is the direction of the force of air resistance?
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UP
What is Newton’s 2nd Law of Motion?
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The acceleration of an object is equal to the net force acting on the object divided by the mass
a = F/m or F = m x a or m = F/a
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A cat pushes a 0.25 kg toy with a net force of 8 N. According to Newton’s 2nd Law, what is the acceleration of the toy?
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a = F/m = 8 N / 0.25 kg = 8/.25 = 32
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What is the difference between a balanced and unbalanced forces?
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Forces acting on an object and combine and form a net force of 0 are balanced forces.
Forces that combine and add to a value that is not 0 are unbalanced forces.
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What is Newton’s 3rd Law of Motion?
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When one object exerts a force on a secondobject, the second object exerts an equal andopposite force on the first object.
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How was Newton’s 3rd law demonstrated inthe balloon lab?
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