(What is the lesson for you, as students? Ask questions! The sooner, the better!)

The fatal pedagogical error is to throw answers, like stones, at the heads of those who have not yet asked the questions. Paul Tillich, American philosopher/theologian (What is the lesson for you, as students? Ask questions! The sooner, the better!)

What is science? Centered in the relationship of concepts (ideas) and experience (action) Ideas guide actions Ideas shape perceptions Experience affects ideas

The Scientific Attitude CHECK YOUR NEIGHBOR Which of these is not a scientific hypothesis? Protons carry an electric charge. Undetectable particles are some of nature s secrets. Charged particles bend when in a magnetic field. All of the above are scientific hypotheses. Explanation: Choices A and C can be disproved by experiments. Choice B has no test for wrongness, so it is not a scientific hypothesis.

Terminology Review Fact a close agreement by competent observers who make a series of observations about the same phenomenon Scientific Hypothesis an educated guess that is only presumed to be factual until supported by experiment Law or principle A hypothesis that has been tested repeatedly and has not been contradicted Theory A synthesis of a large body of information that encompasses well-tested and verified hypotheses about certain aspects of the natural world

More Terminology Force: A push or a pull Inertia: The property of things to resist changes of motion Mass: The measure of an objects inertia; more massive objects are more difficult to make alter straight line motion Weight: The force on an object due to gravity Vector: Quantity that has both magnitude and direction examples: momentum, velocity, force... Scalar: Quantity that can be completely specified by it s magnitude, and has no direction associated with it examples: mass, volume, energy, time...

Aristotle (384-322 BC) Aristotle s views: Some Motion only due to the nature of the object Earth is center of universe Things tend to stop. (Except going in perfect circles around center of universe) Things move because of a mover

Described new observations that didn t agree with the accepted view. Galileo Galilei (1564-1642)

Acceleration Galileo first formulated the concept of acceleration in his experiments with inclined planes.

The Equilibrium Rule The equilibrium rule: The vector sum of forces acting on a nonaccelerating object or system of objects equals zero. Mathematical notation: ΣF = 0.

Equilibrium

Vector Addition + =?

The Equilibrium Rule CHECK YOUR NEIGHBOR The equilibrium rule, ΣF = 0, applies to A. B. C. D. vector quantities. scalar quantities. Both of the above. Neither of the above.

The Equilibrium Rule CHECK YOUR ANSWER The equilibrium rule, ΣF = 0, applies to A. B. C. D. vector quantities. scalar quantities. Both of the above. Neither of the above. Explanation: Vector addition takes into account + and quantities that can cancel to zero. Two forces (vectors) can add to zero, but there is no way that two masses (scalars) can add to zero.

Support Force Support force is force that supports an object on the surface against gravity is also normal force

Support Force aka: Normal Force

Support Force CHECK YOUR NEIGHBOR When you stand on two bathroom scales, with one foot on each scale and weight evenly distributed, each scale will read A. B. C. D. your weight. half your weight. zero. actually more than your weight.

Support Force CHECK YOUR ANSWER When you stand on two bathroom scales, with one foot on each scale and weight evenly distributed, each scale will read A. B. C. D. your weight. half your weight. zero. actually more than your weight. Explanation: You are at rest on the scales, so ΣF = 0. The sum of the two upward

The end

The important thing in science is not so much to obtain new facts as to discover new ways of thinking about them. ~William Lawrence Bragg

Dynamic Equilibrium An object that moves at constant velocity is in equilibrium. When two or more forces cancel to zero on a moving object, then the object is in equilibrium.

Dynamic Equilibrium CHECK YOUR NEIGHBOR A bowling ball is in equilibrium when it A. B. C. D. is at rest. moves steadily in a straight-line path. Both of the above. None of the above.

Dynamic Equilibrium CHECK YOUR ANSWER A bowling ball is in equilibrium when it A. B. C. D. is at rest. moves steadily in a straight-line path. Both of the above. None of the above.

The Force of Friction Friction the resistive force that opposes the motion or attempted motion of an object through a fluid or past another object with which it is in contact always acts in a direction to oppose motion

The Force of Friction Friction (continued) between two surfaces, the amount depends on the kinds of material and how much they are pressed together due to surface bumps and also to the stickiness of atoms on the surfaces of the two materials

The Force of Friction CHECK YOUR NEIGHBOR The force of friction can occur A. B. C. D. with sliding objects. in water. in air. All of the above.

The Force of Friction CHECK YOUR ANSWER The force of friction can occur A. B. C. D. with sliding objects. in water. in air. All of the above. Comment: Friction can also occur for objects at rest. If you push horizontally on your book and it doesn t move, then friction between the book and the table is equal and opposite to your push.

The Force of Friction CHECK YOUR NEIGHBOR When Nellie pushes a crate across a factory floor at constant speed, the force of friction between the crate and the floor is A. B. C. D. less than Nellie s push. equal to Nellie s push. equal and opposite to Nellie s push. more than Nellie s push.

The Force of Friction CHECK YOUR ANSWER When Nellie pushes a crate across a factory floor at constant speed, the force of friction between the crate and the floor is A. B. C. D. less than Nellie s push. equal to Nellie s push. equal and opposite to Nellie s push. more than Nellie s push.

The Force of Friction CHECK YOUR NEIGHBOR When Nellie pushes a crate across a factory floor at an increasing speed, the amount of friction between the crate and the floor is A. B. C. D. less than Nellie s push. equal to Nellie s push. equal and opposite to Nellie s push. more than Nellie s push.

The Force of Friction CHECK YOUR ANSWER When Nellie pushes a crate across a factory floor at an increasing speed, the amount of friction between the crate and the floor is A. B. C. D. less than Nellie s push. equal to Nellie s push. equal and opposite to Nellie s push. more than Nellie s push. Explanation: The increasing speed indicates a net force greater than zero.

Acceleration Galileo first formulated the concept of acceleration in his experiments with inclined planes.

Acceleration Acceleration is the rate at which velocity changes with time. The change in velocity may be in magnitude, in direction, or both. Equation for acceleration: Acceleration = change of velocity time interval

Acceleration Free fall: When the only force acting on a falling object is gravity, (with negligible air resistance), the object is in a state of free fall.

Question: How can we refer to motion without discussing The center of the universe?