Year 7 Forces J.Maden

1. De Lisle Catholic Science CollegeScience departmentKey stage 3 Year 7 Forces J.Maden

2. Forces explorer Click here to see all of the presentation Click here to go directly to mass and weight Click here to go directly to springs Click here to go directly to strong shapes and bridges

3. Introduction to forces • What is a force? • most forces are pushes or pulls • forces cannot be seen but we can see or feel the effects of forces • What can forces do? • start an object moving • stop a moving object • speed up a moving object • slow down a moving object • change the direction of a moving object • change the shape of an object

4. Contact forces • What are contact forces? • forces that need to touch an object before they can exert their effect • Examples of contact forces: • friction eg: air resistance water resistance • upthrust • kicking a football

5. Non-contact forces • What are non-contact forces? • forces that can be exerted on an object from a distance • Examples of non-contact forces: • gravity (weight) • magnetism • static electricity

6. Measuring forces • What is the unit of force? • the unit of force is the newton (N) • one newton of force is about the force that is needed to pick up an apple • What instrument measures force values? • forces can be measured using a forcemeter

7. Forcemeter Scale Adjuster Spring Pointer force has stretched this Reading? 10N Mass

8. The force of gravity • What is gravity? • gravity is a force that pulls masses together • normally the forces are too small to notice • but with a masses as big as stars and planets, the forces becomes large • How big is the Earth’s gravity? • every kilogram of mass on Earth is pulled downwards with a force of about 10N

9. Mass and weight • What does mass measure • the amount of material that an object is made up from • mass is measured in kilograms (kg) • What does weight measure? • the size of the force pulling objects towards the Earth • weight is measured in newtons (N)

10. Weight on the moon Weight on Earth? Weight on Moon? 10N 1.6N Mass on Earth? Mass on Moon? 1kg 1kg

11. Estimating forces 10N 1N 10N 250N 250 000N

12. Using arrows to model forces • Why are arrows good for modelling forces? • forces have two variables: • size and direction • length of the arrow can model the size of the force • direction of the arrow head can model the direction of the force

13. Modelling forces exerted on a moving boat Upthrust caused by Drag (water resistance) caused by Pushing force caused by water friction propeller Pushing force is greater than the drag force How can we tell that the boat is accelerating? Weight caused by gravity

14. Springs • What happens if too much load is added to a spring? • the spring will exceed its elastic limit • What happens when a spring exceeds its elastic limit? • the spring will no longer extend in a uniform way • when the spring is unloaded it will not return to its original length • the spring may even snap

15. Graph to compare the stretching of springs Interpolating from the graph Elastic limits? Elastic limit of the brown spring is ? With a load of 7g blue spring stretched? 5g 7cm

16. Strong shapes • How do corrugations add strength? • corrugations greatly increase the depth of a structure and make it able to carry a greater load • What is a cantilever? • a cantilever is a beam or girder fixed at one end • most material is concentrated near the fixed ends

17. Strong shapes in nature Diplodocus neck and tail cantilevered Scallop shell corrugated

18. Bridge design • Good design features? • use of cantilevers • use of the arched-shape • use of triangles

19. Year 7Forces The end Click here to view again