1. Boardworks Ltd 20041 of 20 Boardworks Ltd 20061 of 27 KS3 Physics 7K Forces and their Effects

2. Boardworks Ltd 20041 of 20 Boardworks Ltd 20062 of 27 7K Forces and their Effects Contents Feel the force Weight and mass Forces in water Friction Summary activities 3. Boardworks Ltd 20041 of 20 Boardworks Ltd 20063 of 27 A force is a push, pull or twist. A force cannot be seen but you can see how a force affects an object. What is a force? 4. Boardworks Ltd 20041 of 20 Boardworks Ltd 20064 of 27 Forces activity 5. Boardworks Ltd 20041 of 20 Boardworks Ltd 20065 of 27 10 N 10 N If you link two forcemeters and pull equally hard from both ends, the forces recorded on both will be the same. balanced forces When forces are balanced The forces acting on the central hooks cancel each other out they are equal in magnitude and opposite in direction. Because the forces are balanced the hooks do not move. 6. Boardworks Ltd 20041 of 20 Boardworks Ltd 20066 of 27 11 N 10 N What happens if the pull on one end is greater than the pull on the other end? unbalanced forces movement When forces are unbalanced The forces acting on the hooks are no longer balanced. Both hooks will start to move to the left their speed will change. This is called acceleration. Unbalanced forces lead to a change in speed or direction. 7. Boardworks Ltd 20041 of 20 Boardworks Ltd 20067 of 27 Balanced or unbalanced forces? 8. Boardworks Ltd 20041 of 20 Boardworks Ltd 20068 of 27 7K Forces and their Effects Contents Feel the force Weight and mass Forces in water Friction Summary activities 9. Boardworks Ltd 20041 of 20 Boardworks Ltd 20069 of 27 If you rub your hands together they get warm. There is resistance to the rubbing motion. What is the name of this resistive force called? What causes this force? Your hands might look smooth, but on a microscopic level they have rough surfaces. So when you rub your hands together you feel the resistive force of friction. What is friction? It is called friction. 10. Boardworks Ltd 20041 of 20 Boardworks Ltd 200610 of 27 Friction always tries to slow moving objects down. We say it opposes motion. There is a maximum value for the frictional force which depends on: More about friction Friction is created whenever two touching objects or surfaces move past each other. Friction also occurs when things move through air. This is called air resistance or drag. the force pushing the two surfaces together; the state of the surfaces in contact. 11. Boardworks Ltd 20041 of 20 Boardworks Ltd 200611 of 27 One more? Probably the most important Label all sources of friction that can act on this bike. tyre and road brake pad and rim wheel bearing wheel bearing pedal bearing links in chain air resistance or drag What are the sources of friction? 12. Boardworks Ltd 20041 of 20 Boardworks Ltd 200612 of 27 Effect of frictional forces 13. Boardworks Ltd 20041 of 20 Boardworks Ltd 200613 of 27 7K Forces and their Effects Contents Feel the force Weight and mass Forces in water Friction Summary activities 14. Boardworks Ltd 20041 of 20 Boardworks Ltd 200614 of 27 upthrust frictionthrust weight What is thrust? The force that pushes an object forward. What is upthrust? The force that pushes an object upwards in a liquid or a gas, also called buoyancy. Forces in water 15. Boardworks Ltd 20041 of 20 Boardworks Ltd 200615 of 27 Ferry forces 16. Boardworks Ltd 20041 of 20 Boardworks Ltd 200616 of 27 What happens to the weight of the ship? What happens to the upthrust on the ship? Which is the largest force - weight or upthrust? increases both equal increases The ferry arrives at Calais and is loaded with travellers. Changing forces 17. Boardworks Ltd 20041 of 20 Boardworks Ltd 200617 of 27 7K Forces and their Effects Contents Feel the force Weight and mass Forces in water Friction Summary activities 18. Boardworks Ltd 20041 of 20 Boardworks Ltd 200618 of 27 Mass and weight are not the same! What are mass and weight? Mass is the amount of matter in an object and is measured in kilograms. Mass is not a force. Weight is a force and is caused by the pull of gravity acting on a mass. Like other forces, weight is measured in newtons and has both magnitude and direction. Mass will have the same value anywhere in the Universe, including outer space. Weight has different values depending on where you are in the Universe. 19. Boardworks Ltd 20041 of 20 Boardworks Ltd 200619 of 27 Weight and mass on the Moon The force of gravity is less on the Moon than it is on Earth. This is because the Moon has a smaller mass than the Earth. However, the astronaut still has the same body and the same mass: he just weighs less because gravity is weaker on the Moon. Any object will weigh less on the Moon than it does on Earth. An astronaut could jump 20 feet into the air on the Moon because gravity is less. 20. Boardworks Ltd 20041 of 20 Boardworks Ltd 200620 of 27 A scientist should never say: She weighs 50 kilograms, but should always say: Talking about weight and mass She has a mass of 50 kilograms. Her weight is about 500 newtons. Alternatively, the scientist could say: The gravitational force acting on her mass is about 500 newtons. This is the same as saying: 21. Boardworks Ltd 20041 of 20 Boardworks Ltd 200621 of 27 Weight and mass on different planets 22. Boardworks Ltd 20041 of 20 Boardworks Ltd 200622 of 27 Weight or mass? 23. Boardworks Ltd 20041 of 20 Boardworks Ltd 200623 of 27 7K Forces and their Effects Contents Feel the force Weight and mass Forces in water Friction Summary activities 24. Boardworks Ltd 20041 of 20 Boardworks Ltd 200624 of 27 Glossary air resistance A frictional force that acts against an object moving through air. force A push or a pull, measured in newtons (N). friction A force that occurs between two surfaces rubbing against each other. gravity The force of attraction between two objects. mass The amount of matter that an object is made of, measured in kilograms (kg). thrust A force that pushes an object forwards. upthrust A force that pushes an object upwards. weight The force caused by gravity acting on an object, measured in newtons (N). 25. Boardworks Ltd 20041 of 20 Boardworks Ltd 200625 of 27 Anagrams 26. Boardworks Ltd 20041 of 20 Boardworks Ltd 200626 of 27 Missing words 27. Boardworks Ltd 20041 of 20 Boardworks Ltd 200627 of 27 Multiple-choice quiz