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Flashback: Newtons Laws of Motion Sir Isaac Newton was a central figure in the Scientific Revolution during the 17 th century. His ideas went against the more accepted ideas of motion. The popular idea before Newton was that a moving object, if left on its own, would eventually come to rest, and a force was necessary to keep the object moving. We now know this to be false, thanks to Isaac Newton.

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Flashback: Newtons Laws of Motion Today, Newtons three laws of motion are considered to be the backbone of physics. These ideas were major breakthroughs that set history on a new course. Because of these ideas we now have safety restraints (seat belts) in multiple types of travel.

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Flashback: Newtons 1 st Law of Motion An object at rest remains at rest, and an object in motion remains in motion at a constant speed and in a straight line unless acted on by an unbalanced force. Newtons 1 st law is sometimes called the law of inertia. Inertia is the tendency of all objects to resist any change in motion.

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Law of Intertia Tennis ball wants to keep sitting still Baseball wants to keep moving!

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Mass is a measure of inertia Small mass = less inertia Large mass = more inertia Law of Intertia, continued

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Dont let this be you. Wear seat belts!! Because of inertia, objects (including you) resist changes in their motion. When the car going 80 km/hour is stopped by the brick wall, your body keeps moving at 80 km/hour. Law of Intertia

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Flashback: Newtons First Law Balanced Forces = No Change in Velocity A stationary object will never move without unbalanced forces acting on it Balanced forces = no change in speed 12N 0N A moving object will never stop moving without unbalanced forces acting on it

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If the forces are in the same direction, then the net force is the sum between the two forces. 12 N8 N NET FORCE = 12N + 8N = 20N, left Combining forces to form NET FORCE

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If two forces are in opposite directions, then the net force is the difference between the two forces, and it is in the direction of the larger force. 12 N8 N NET FORCE = 12N – 8N = 4N, right

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Flashback: Types of Friction – Static Friction Static friction is the type of friction that prevents an object from moving when a force is applied. For example, when you push or pull on the refrigerator and at first it doesnt want to move but then it suddenly starts to move.

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Flashback: Types of Friction – Static Friction Generally, the rougher the surface or the heavier the object, the more static friction.

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Sliding friction slows down an object that slides. Sliding friction is due to microscopic roughness of two surfaces. Brakes on a car are an example of sliding friction. Flashback: Types of Friction - Sliding Friction

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Rolling friction is needed to provide grip to make a wheel or a tire turn. Rolling friction occurs between the ground and the part of the tire touching the ground. Flashback: Types of Friction - Rolling Friction

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Fluid Friction occurs between an object and air or water. For example, fluid friction occurs when skydivers jump out of a plane, or when boats travel through the water Flashback: Types of Friction - Fluid Friction

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Flashback: Mass vs. Weight Mass is the amount of matter in an object and DOES NOT change with gravity. Mass is measured in Kilograms (Kg). Weight is a force measured by the pull of the Earths gravity. Weight is measure in Newtons (N).

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Your weight would change if you were standing on a planet other than Earth, as shown. Flashback: Mass vs. Weight If your mass was 60 kg, what would your weight in Newtons be on Earth? On Jupiter?

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When the motion of an object changes, the object is accelerating. Acceleration occurs any time an object speeds up, slows down, or changes its direction of motion. Flashback: Force and Acceleration

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Newtons 2 nd Law of Motion The acceleration of an object depends on the mass of the object and the amount of force applied (f=ma) Newtons 2 nd law of motion connects force, acceleration, and mass. In the presence of a NET FORCE, an object experiences acceleration in the direction of the force.

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Newtons 2 nd Law of Motion With any given force: an object with less mass accelerates quicker (i.e. volleyball) An object with more mass accelerates slower (i.e. bowling ball)

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Your _______ on Earth is the gravitational force between you and Earth. A. acceleration B. inertia C. mass D. weight Question 1

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Answer The answer is D, weight. Since weight is dependant on gravity, your weight would be different if you were standing on a planet other than Earth. Question 1

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Question 2 Explain Newtons second law of motion.

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Newtons Second Law states that an object acted upon by a net force will accelerate in the direction of the force. And, that the net force is equal to the acceleration times the mass of the object (f=ma). ANSWER Question 2

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Newtons 2 nd Law Formulas f = ma m = f / aa = f / m ALL THESE ARE DIFFERENT WAYS TO EXPRESS THE SAME EQUATION!! In these equations, a is the acceleration (m/s 2 ), m is the mass (kg), and f is the net force (N). Force is measured in Newtons, abbreviated N.

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Calculations, Force Newtons second law of motion can be used to calculate NET FORCE. A baseball has a mass of 0.2 kg. If its acceleration is 40 m/s 2, what is the net force on the baseball? f = ma f = ? m = 0.2kg a = 40m/s 2 f = 0.2kg * 40m/s 2 f = 8 N f = ma

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Calculations, Force A 6 kg cat accelerates at 1.5 m/s 2. Find the net force. f = ma f = ? m = 6kg a = 1.5m/s 2 f = 6kg * 1.5m/s 2 f = 9 N

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(Advanced Classes) Calculations, Force A 2 kg book is pushed along a table with a thrusting force of 4 N. Find the frictional force on the book if the books acceleration is 1.5 m/s 2 f = ma f = ? m = 2kg a = 1.5m/s 2 f = 2kg * 1.5m/s 2 f = 3 N (net force) 4 N (thrusting force) – 3 N (net force) = 1 N (frictional force) f = ma

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Calculations, Acceleration Newtons second law of motion can be used to calculate ACCELERATION. Suppose you pull a 10-kg sled so that the net force on the sled is 5 N. What is the acceleration? f = ma f = 5N m = 10kg a = ? 5N = 10kg * a 0.5 m/s 2 f = ma a = 5N/10kg =

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Calculations, Acceleration A net force of 4,500 N acts on a car with a mass of 1,500 kg. What is the acceleration of the car? f = ma f = 4,500N m = 1,500kg a = ? 4500N = 1500kg * a 3.0 m/s 2 f = ma a = 4500N/1500kg =

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Calculations, Acceleration A book with a mass of 2.0 kg is pushed along a table. If the net force on the book is 1.0 N, what is the acceleration of the book? f = ma f = 1.0N m = 2.0kg a = ? 1.0N = 2.0kg * a 0.5 m/s 2 f = ma a = 1.0N/2.0kg =

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Calculations, Mass Newtons second law of motion can also be used to calculate MASS. A basketball is thrown with a net force of 9 N and accelerates at 1.5 m/s 2, what is the mass of the basketball? f = ma f = 9N m = ? a = 1.5 m/s 2 9N = m * 1.5m/s 2 6 kg f = ma m = 1.5m/s 2 / 9N =

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Calculations, Mass An object acted on by a force of 3.6 N has an acceleration of 1.2 m/s 2. What is the mass of the object? f = ma f = 3.6N m = ? a = 1.2 m/s 2 3.6N = m * 1.2m/s 2 3 kg f = ma m = 3.6N / 1.2m/s 2 =

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