forces ppt.ppt
- 1. CIE IGCSE Specification 1.5.1 Effects of Forces Core • State that a force may produce a change in size and shape of a body • Plot extension/load graphs and describe the associated experimental procedure Supplement • Interpret extension/load graphs • State Hooke’s Law and recall and use the expression F = k x F= Force k = spring constant x= extension length • Recognise the significance of the term ‘limit of proportionality’ for an extension/load graph
- 2. EFFECTS OF FORCES • FORCE CAN MAKE A STATIONARY OBJECT MOVE • FORCE CAN STOP A MOVING OBJECT • FORCE CAN CHANGE THE SPPED • FORCE CAN CHANGE THE DIRECTION • FORCE CAN CHANGE THE SHAPE
- 3. Elastic materials return to their original shape when the forces on them are removed. Plastic materials retain their new shape.
- 4. Stretching Springs Experimental procedure: 1. Place the weight holder only on the spring and note the position of the pin against the metre rule. The original length (lo) 2. Add 1N (100g) to the holder and note the new position of the pin. The new length (l) 3. Calculate the extension of the spring. (l - lo) 4. Repeat stages 1 to 3 for 2N, 3N, 4N, 5N, 6N and 7N. metre rule pin spring weights https://phet.colorado.edu/sims/html/masses-and-springs- basics/latest/masses-and-springs-basics_all.html
- 5. Typical results Pin position with holder only (unstarched length l0 ) /cm Added weight or Force, F /N Pin position with weight (New length, l) /cm Extension (l-lO)/cm 45 1 48 3 45 2 51 6 45 3 54 9 45 4 57 12 45 5 60 15 45 6 64 19 45 7 70 22
- 7. Force against extension graph if the elastic limit is exceeded 0 Force (N) 0 Extension (mm) Limit of proportionality
- 8. 0 2 4 6 8 10 12 0 0.2 0.4 0.6 0.8 1 1.2 Force (N) Extension Force -Extension Graph
- 9. Force against extension graph 0 Force (N) 0 Extension (mm)
- 10. Hooke’s law Hooke’s law states that the extension of a spring force is proportional to the force used to stretch the spring with in the limit of proportionality. ‘Proportional’ means that if the force is doubled then the extension also doubles. The line on a graph of force against extension will be a straight AND go through the origin.
- 13. 0 2 4 6 8 10 12 0 0.2 0.4 0.6 0.8 1 1.2 Force (N) Extension Force - Extension Graph stiffer spring
- 15. Question A spring of original length 150mm is extended by 30mm by a force of 4N. Calculate the length of the spring if a force of 12N is applied. 12N is three times 4N Therefore the new extension should be 3 x 30mm = 90mm New spring length = 150mm + 90mm = 240mm
- 16. Elastic limit Up to a certain extension if the force is removed the spring will return to its original length. The spring is behaving elastically. If this critical extension is exceeded, known as the elastic limit, the spring will be permanently stretched. Hooke’s law is no longer obeyed by the spring if its elastic limit is exceeded. The right hand spring has been stretched beyond its elastic limit
- 17. Hooke’s Law Glossary • Elastic materials return to their original shape when the forces on them are removed. • Plastic materials retain their new shape, when forces are removed • Hooke’s Law - The extension of a spring or wire is directly proportional to the force applied provided the limit of proportionality is not exceeded. • Spring constant is the gradient of the force (x- axis) against extension (y-axis) the gradient is the spring constant Units N/m • A stretching force puts an object such as a wire or spring under tension • The limit of proportionality is the is the point beyond which Hooke’s law is no longer true when stretching a material. • The elastic limit is the point beyond which the material you are stretching becomes permanently stretched so that the material does not return to its original length when the force is removed.
- 18. Choose appropriate words to fill in the gaps below: Hooke’s law states that when a wire or spring is _________ the increase in length or _________ is proportional to the load ______ applied. This law is not obeyed if the spring is taken beyond its ______ limit after which it will become _____________ stretched. A ________ band does not obey Hooke’s law. A graph illustrating Hooke’s law will have a line that is ___________ and passes through the _______. straight elastic origin stretched rubber force extension WORD SELECTION: permanently straight elastic origin stretched rubber force extension permanently
- 19. Online Simulations Effect of forces on motion using a space module - Freezeray.com Force combination balloon game - eChalk Electric & Magnetic Forces - 'Whys Guy' Video Clip (3:30mins) - Shows Charged Balloon & Effect of a magnet on a TV screen. Resultant of two forces - Fendt Forces on objects immersed in liquids - NTNU BBC KS3 Bitesize Revision: What is a force Balanced forces Unbalanced forces BBC AQA GCSE Bitesize Revision: Resultant force Types of forces Vector Addition - PhET - Learn how to add vectors. Drag vectors onto a graph, change their length and angle, and sum them together. The magnitude, angle, and components of each vector can be displayed in several formats. Representing vectors - eChalk Vectors & Scalars - eChalk Vector addition - eChalk Vector Chains - eChalk Fifty-Fifty Game on Vectors & Scalars - by KT - Microsoft WORD Vector addition - Explore Science Stretching Springs - PhET - A realistic mass and spring laboratory. Hang masses from springs and adjust the spring stiffness and damping. You can even slow time. Transport the lab to different planets. A chart shows the kinetic, potential, and thermal energy for each spring.