Quick Recap A brass object consists of 3
Quick Recap A brass object consists of 3. 3 x 10 -5 m 3 of copper and 1. 7 x 10 -5 m 3 of zinc. Calculate the mass and the density of this object. The density of copper = 8900 kgm-3. The density of zinc = 7100 kgm-3.
Quick Recap
A LEVEL PHYSICS Year 1 Hooke’s Law A* A B C I can use Hooke’s Law to calculate force, extension and the spring constant (grade c) I can use Hooke’s Law to calculate force extension and k in combinations of springs (grade b) I can explain the potential energy stored in a spring and relate this to Hooke’s Law (grade a) B/C Target A/A* Target EP EP AEP EP
Hooke In the 1600 s, a scientist called Robert Hooke discovered a law for elastic materials. Hooke's achievements were extraordinary - he made the first powerful microscope and wrote the first scientific bestseller, Micrographia. He even coined the word ‘Cell’.
Hooke’s Law • Stretched springs experience a change in length • This is the extension from the rest position Hooke’s Law states that the force needed to stretch a spring is directly proportional to the extension of the spring from its natural length
Hooke’s Law The greater the value of k, the stiffer the spring Units= Nm-1
The elastic limit can be seen on the graph. This is where it stops obeying Hookes law.
Tension, T Extension, ΔL Describe the relationship between Tension and extension
Tension, T Extension, ΔL Straight line graphs through the origin This means it is directly proportional What happens when a spring is stretched beyond its elastic limit? Will it obey Hooke’s Law?
Quick Question A vertical steel spring fixed at its upper end has an unstretched length of 300 mm. Its length is increased to 385 mm when a 5. 0 N weight attached to the lower end is at rest. Calculate: a) The spring constant b) The length of the spring when it supports an 8. 0 N weight.
Quick Question
Quick Question
Springs In Parallel P Q
Springs in Series P Q
Force, F Extension, ΔL
Force, F Extension, ΔL
Spring Constant • The spring constant measures how stiff the spring is. • The larger the spring constant the stiffer the spring. • You may be able to see this by looking at the graphs below: k is measured in units of newtons per metre (Nm -1).
Key Definitions • Hooke’s Law = The amount a spring stretches is proportional to the amount of force applied to it. • The spring constant measures how stiff the spring is. The larger the spring constant the stiffer the spring. • A Diagram to show Hooke’s Law F=k∆x
Further Study: To Watch • The story of scientist Robert Hooke and the jealous rival who erased him from public consciousness after his death - Isaac Newton. • Newton plagiarised Hooke and conspired to destroy his reputation. Robert Hooke was "robbed of the credit" for the inverse square law of gravity and wiped from the pages of history. No wonder Newton never had a mechanism. • Hooke's achievements were extraordinary - he made the first powerful microscope and wrote the first scientific best-seller, Micrographia. • A drama revealing the extraordinary, prolific, bizarre and conflict-riddled life of Robert Hooke, one of the greatest scientists in English history, on the tercentenary of his death.
Further Study: To Read • The Curious Life of Robert Hooke: The Man Who Measured London • Author: Lisa Jardine • Publisher: Harper Perennial • Publication date: February 1, 2005
Bibliography • K Johnson et al (2000) Advanced Physics for You. Nelson Thornes Ltd. • England's Leonardo: Robert Hooke and the Seventeenth -century Scientific Revolution, Allan Chapman. Institute of Physics Publishing, 2004 • http: //www. s-cool. co. uk/alevel/physics/deformationof-solids/hookes-law. html#hookes-law • http: //forum. esoft. in/misc-tv-videos/71356 -bbc-fourrobert-hooke-victim-genius-2009 -a. html (For Information on Hooke vs Newton video)
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