chapter 2: force and newton’s laws. section 1 newton’s first law a.force – push or pull on an...
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Chapter 2: Force and Newton’s Laws
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Section 1 Newton’s First Law
A. Force – push or pull on an object1. The combination of all the forces acting on an
object is the net force
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2. When forces are balanced forces, they cancel each other out and do not change an object’s motion; when forces are unbalanced forces, the motion of an object changes.
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B. Newton’s first law of motion – an object will remain at rest or move with constant speed unless a force is applied
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C. Friction is a force that resists sliding between two touching surfaces or through air or water1. Friction slows down an object’s motion2. Static friction – the type of friction that prevents
an object from moving when a force is applied3. Sliding friction is due to the microscopic
roughness of two surfaces; it slows down a sliding object
4. Rolling friction between the ground and a wheel allows the wheel to roll
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Write down where is friction is at work
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Section 2 Newton’s second Law
A. Newton’s second law of motion connects force, acceleration, and mass; it explains that an object acted upon by a force will accelerate in the direction of the force; acceleration equals net force divided by mass.
Acceleration = net force / mass
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• Units of Force– Measured in newtons (N)– Equal to mass x acceleration (kg x m/s2)
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B. Gravity – attractive force between two objects; depends on the mass of the objects and distance between them; gravitational force is also called weight.
Weight: F= ma = m x (9.8 m/s2) *your weight is the gravitational force
between you and the Earth
Mass and weight are different!
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C. The second law explains how to calculate the acceleration of an object if its mass and the forces acting on it are both known
Acceleration = net force / mass = N/kg = (kg x m/s2 )/kg = m/s2
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D. In circular motion, the centripetal force is always perpendicular to the motion
motion
force
What does perpendicular mean?
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E. Terminal velocity is reached when the force of gravity is balanced by air resistance; the size of the air resistance force depends on the shape of an object and its speed• Air resistance = air pushing against an object’s motion
– A form of friction
• The force of air resistance pushing up on the object is increasing as the object moves faster
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F. An object can speed up, slow down, or turn in the direction of the net force when unbalanced forces act on it
Speeding Up – force in same direction as motionSlowing Down – force in opposite direction as motionTurning- force at an angle to direction of motion
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Section 3 Newton’s Third Law
A. Newton’s third law of motion states that forces always act in equal but opposite pairs; for every action there is an equal and opposite reaction
B. Action-reaction forces are always the same size but are in opposite directions and act on different objects.
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1. When the mass of one object is considerably larger than the mass of another object, the action-reaction force is not noticeable
2. Air and water exert action-reaction forces with objects such as hands or canoe paddles
3. A rocket launches due to the equal but opposite forces of the burning fuel.
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• Weightlessness– The condition that occurs in free fall when the
weight of an object seems to be zero– Free fall = when the only force acting on a falling
object is gravity• With no force pushing up on you, you have no
sensation of weight