Presentation on theme: "Wednesday, Jan. 27 th Agenda Homework Questions/problems/collect Begin section 7.3: Newton’s Laws of Motion –Newton’s 1 st law, inertia, Newton’s 2 nd."— Presentation transcript:
Wednesday, Jan. 27 th Agenda Homework Questions/problems/collect Begin section 7.3: Newton’s Laws of Motion –Newton’s 1 st law, inertia, Newton’s 2 nd law In-Class assignment: –Pg. 236, practice #1-3 Movie: “Laws of Motion” Homework: “The Great Plague and Isaac Newton” worksheet
Section 7.3: Newton’s Laws of Motion Every motion you see or experience is related to a force. Sir Isaac Newton described the relationship between motion and force in 3 laws that we now call Newton’s Laws of Motion
Newton’s 1 st Law Newton’s First Law: An object at rest remains at rest and an object in motion maintains its velocity unless it experiences an unbalanced force.
Newton’s 1 st Law You experience Newton’s 1 st law when you ride in a car. As the car comes to a stop, you can feel your body continue to move forward. Your seat belt and the friction between your pants and the seat stop your forward motion. They provide the unbalanced rearward forces needed to bring you to a stop as the car stops.
Inertia Inertia: the tendency of an object to remain at rest or in motion with a constant velocity All objects have inertia because they resist changes in motion.
Newton’s 2 nd Law Newton’s Second Law: The unbalanced force acting on an object equals the object’s mass times its acceleration. Force = (mass) X (acceleration) F = ma
Newton’s 2 nd Law Just like we did before, we can rearrange the equation F = ma to solve for different things. To solve for acceleration: a = F m To solve for mass: m = F a
Newton’s 2 nd Law Force = mass X acceleration
Force is Measured in Newtons Newton (N): the SI unit of force 1 Newton is the force that can give a mass of 1 kg an acceleration of 1 m/s 2. 1 N = 1 kg X 1 m/s 2 1 N = pounds 1 pound = N
Newton’s 2 nd law example, pg 236 Zookeepers lift a stretcher that holds a sedated lion. The total mass of the lion and stretcher is 175 kg, and the lion’s upward acceleration is m/s 2. What is the unbalanced force necessary to produce this acceleration of the lion and the stretcher? Equation: Force = mass X acceleration Mass = 175 kg Acceleration = m/s 2 Solve: Force = 175 kg X m/s 2 = 115 kg∙m/s 2 = 115 N
Newton’s 2 nd law example #2 Assume that a catcher in a professional baseball game exerts a force of 65.0 N to stop a ball. If the baseball has a mass of kg, what is its acceleration as it is being caught? Equation: a = F m Force = 65.0 N Mass = kg Solve: a = 65.0 N = 448 m/s kg
Newton’s 2 nd law example #3 A whale shark is being lifted by a crane for transport to an aquarium. The crane uses a force of 25,000 N to lift the shark. If the shark’s acceleration is 1.25 m/s 2, what is the shark’s mass? Equation: m = F a Force = 25,000 N Acceleration: 1.25 m/s 2 Solve: m = 25,000 N = 20,000 kg 1.25 m/s 2
In-Class Assignment Practice problems, pg. 236, # 1-3
Movie “Laws of Motion”
Homework Worksheet: “The Great Plague and Isaac Newton”