Students will develop a theoretical explanation (based on Newton’s
second law) that explains why heavier objects do not accelerate at a rate
different from that of lighter objects.
Students will work with dynamics carts and suitable spring scales to determine
the principle relating force and acceleration.
Students will quantify the above relationship (Newton’s 2nd law) by
conducting an experiment in which all extraneous variables are controlled.
Students will resolve the traditional Newton’s 3rd law paradox (horse
and cart problem). The problem of the tug-of-war can be used to examine Newton’s
third law, and give some physical meaning to the idea of “equal and
opposite” forces. Have two students with large spring scales pull on
opposite ends of a rope. Tell the first student to pull “hard”
(as shown by the first spring scale), and the second student to pull “not
so hard” (as shown by the second spring scale). Regardless of how hard
either student pulls, the scales will always read the same. This is what Newton’s
third law is all about. Pose the question, “If the students are both
pulling with equal and opposite force (which is clear from the readings of
the two spring scales), then how is it possible that one student can ever
expect to win over the other in a tug-of-war competition?
3.2 Buoyant Force
Students will identify factors that might influence buoyancy (e.g., depth,
orientation, density, composition, etc.) and devise and conduct experiments
to test the various factors’ influence on buoyancy to determine which
might affect the buoyant force.
Student will design and conduct experiments to determine the independently
the relationships between buoyancy and pertinent factors that affect buoyancy
to determine the basic principles and mathematical nature of those relationships.
Students will establish and verify the law of buoyancy through suitable
experimental means.
Students will hypothesize as to the source of the buoyant force, and will
mathematically attempt to derive the experimental form of the law of buoyancy.
Students will determine the relationship between the buoyant force and
the weight of the liquid in which an object is immersed.
Students will, using their knowledge of the law of buoyancy, determine
the fraction of a floating body (e.g., an iceberg) above and below the surface
of a liquid.
Students will determine the relationship between the density of an object
and the density of the liquid it is immersed in as it relates to floating,
sinking, and neutral buoyancy.
Students will explain why, when an object is suspended in a liquid, that
the weight of the combination is equal to the weight of the fluid plus the
buoyant force (e.g., when a tea bag is suspended in a cup of hot water, the
weight of the cup and water increases by an amount equal to the buoyant force
on the tea bag.)
3.3 Friction
Students will create and conduct an experiment to determine what effect
the mass of an object has on the sliding force of friction on a horizontal
surface.
Students will create and conduct an experiment to determine what effect
the surface area of an object has on the sliding force of friction on a horizontal
surface.
Students will create and conduct an experiment to determine what effect
the roughness of a surface has on the sliding force of friction on a horizontal
surface.
Students will use a variable-angle inclined plane as well as a force diagram
to determine the coefficient of static friction.
Students will use a sliding block of constant speed and a scale to determine
the coefficient of kinetic friction.
Students will, using an acoustical motion detector, determine the terminal
velocity of a falling coffee filter, and determine the force of drag.
Students will develop a theoretical explanation for the reason why surface
area does not affect the force of friction (e.g. a block sliding on its side
has the same force of friction as it would if the block were sliding on its
end).
3.4 Torque
Students will find the relationship between force and distance in first-class,
second-class, and third-class levers.
Students will find the principles of torque related to a simple balance
(e.g., F1d1 = F2d2)
by varying the mass and distance on only one side of a balance.
Students will find the relationship between “work in” and “work
out” of a first class lever.
Students will find the relationship between torque and angular acceleration
of a rotating object with a known moment of inertia.
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