Physics (NSC013)
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Here are 3 examples for each of Newton's Laws of Motion: 1st Law (Inertia): - A car at rest stays at rest unless a force acts on it. - A ball rolling across a table will keep rolling at the same speed and direction unless something stops it or changes its motion. - An object in motion in outer space will stay in motion with the same speed and direction unless another force interacts with it. 2nd Law (F=ma): - The harder you push on a heavy box, the slower it will accelerate compared to a lighter box with the same push. - A rocket accelerates faster as it burns fuel and loses mass over time. - Braking
Physics (NSC013)
- 1. NSC 013 Physics Marie Jessica B. Alumaga
- 2. Objectives • To describe the different branches of classical physics • To appreciate the contributions of different scientists in the field of physics • To explain the different ways of describing motion • To state the three laws of motion and be able to solve problems involving motion
- 3. Physics - study of matter, energy, space and time - divided into two main branches • Classical physics • Modern physics
- 4. Branches and Sub-branches of Classical Physics A. Mechanics - the study of forces acting on bodies, whether at rest or in motion Statics – about forces acting on bodies at rest Kinematics – about motion without regard to its cause Dynamics – about motion and forces that affect it
- 5. Branches and Sub-branches of Classical Physics B. Acoustics - the study of the production and propagation of sound waves
- 6. Branches and Sub-branches of Classical Physics C. Optics – the study of light • Physical optics – production, nature and properties of light • Physiological optics – part played by light in vision • Geometrical optics – reflection and refraction of light as encountered in the study of mirrors and lenses
- 7. Branches and Sub-branches of Classical Physics D. Thermodynamics – study of the relationship between heat and other forms of energy
- 8. Branches and Sub-branches of Classical Physics E. Electromagnetism – study of the properties of electric current and magnetism, and their relationship • Electrostatics – electric charges at rest • Electrodynamics – moving charges • Magnetostatics – magnetic poles at rest
- 9. Aristotle ((384 BC – 322 BC) According to him, motion has two kinds: a. Natural motion – thought to be either straight up or straight down b. Violent motion – imposed motion, Marble bust of Aristotle. Roman result of forces which pushed or copy after a Greek bronze original by Lysippus c. 330 BC. pulled
- 10. Archimedes (287 BC – 212 BC) - used buoyancy determined whether the golden crown was less dense than solid gold - introduced the screw to raise water efficiently - used mirrors acting collectively as a parabolic reflector to burn ships attacking Syracuse - introduced the lever Give me a place to stand on, and I will move the Earth.
- 11. Galileo Galilei (1564 – 1642) - first to use a telescope - devised and improved the geometrical and military compass - formulated the basic law of falling bodies ‘all things fall at the same rate’ Galileo's geometrical and A replica of the earliest military compass surviving telescope
- 12. Sir Isaac Newton (1643 – 1727) - lectured on optics - built the first practical reflecting telescope - introduced the universal law of gravitation - stated the three laws of motion A replica of Newton's second Reflecting telescope that he presented to the Royal Society in 1672[
- 13. Newton's law of universal gravitation states that every massive particle in the universe attracts every other massive particle with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between them
- 14. Newton's law of universal gravitation F magnitude of the gravitational force between the two point masses, N G gravitational constant, 6.674×10−11 N m2 kg−2 m1 mass of the first point mass, kg m2 mass of the second point mass, kg R distance between the two point masses, m
- 15. Newton's law of universal gravitation How can the mass of the earth be determined using an apple? This illustrates the way scientists can use indirect methods to perform seemingly “impossible tasks” GmM Gravitational force on apple = F = 2 ÷ R gR 2 (9.8m / s 2 )(6.4 ×106 m) 2 M = ÷ = = 6 × 1024 kg G 6.67 ×10−11 N ×m 2 / kg 2
- 16. MOTIO N Speed the rate at which something moves a given distance s = distance/time Velocity • a vector quantity that includes both speed and direction v = distance/time Acceleration of an object • the rate of change of its velocity • for straight-line motion, average acceleration is the rate of change of speed a = velocityf – velocityi/t
- 19. Newton’s first law of motion (Law of Inertia) Inertia is a term used to measure the ability of an object to resist a change in its state of motion. An object with a lot of inertia takes a lot of force to start or stop; an object with a small amount of inertia requires a small amount of force to start or stop. The word “inertia” comes from the Latin word inertus, which can be translated to mean “lazy.”
- 20. Newton’s Second Law of Motion (Law of Acceleration) The acceleration of an object is equal to the force applied divided by the mass of the object. a=F m
- 21. Newton’s Second Law of Motion (Law of Acceleration) If more force is applied to an object, the object accelerates at a higher rate.
- 22. Newton’s Second Law of Motion (Law of Acceleration) If an object has more mass it accelerates at a lower rate because mass has inertia.
- 24. Newton’s Second Law of Motion (Law of Acceleration) Sample problem 1 A cart rolls down a ramp. The cart has a mass of 500 grams (0.5 kg). Using a spring scale, you measure a net force of 2 newtons pulling the car down. Calculate the acceleration of the cart. Solution: Answer: 4 m/s2 a = F/m = 2 N/0.5 kg = 4 m/s2
- 25. Newton’s Second Law of Motion (Law of Acceleration) Sample problem 2 An airplane needs to accelerate at 5 m/sec2 to reach take-off speed before reaching the end of the runway. The mass of the airplane is 5,000 kilograms. How much force is needed from the engine? Solution: F = ma Answer: 25,000N = 5,000kg(5m/s2) = 25,000N
- 27. Newton’s third Law of Motion (Action-reaction) “For every action there is an equal and opposite reaction.” Newton’s third law discusses pairs of objects and the interactions between them.
- 28. Newton’s third Law of Motion (Action-reaction) More examples
- 29. Newton’s third Law of Motion (Action-reaction) Sample problem Three people are each applying 250 N of force to try to move a heavy cart. The people are standing on a rug. Someone nearby notices that the rug is slipping. How much force must be applied to the rug to keep it from slipping? Sketch the action and Answer: 750N reaction forces acting between the people and the cart and between the people and the rug.
- 30. Homework: (Use half cross-wise.) Give three (3) examples of each of the Newton’s Laws of motion