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Physics-Force new.pptx igcse newton gravity
- 2. Example of Force Force to push car Force to pull a drawer open Force to stretch a rubber band Force to turn a door handle
- 3. Definition A force is a push or pull that can change the shape of an object or change the way that it moves Keywords : A forces changes its shape, speed and direction If something start to move or speeds up a force is acting on it Forces can also slow things down or stop them to moving Forces can change the direction of motion
- 4. Force Cannot be Seen We cant see the forces but we can feel their effects. Sit on a chair, you can feel the upward push of the chair. Force arrow is used to show the direction of a force.
- 5. Force Arrow Forces act on objects to push, pull, stretch, and turn. Forces happen when two objects interact with each other. A force arrow shows the direction of a force. Push of woman on trolley The woman and trolley interact The force arrow is labeled to show which object is doing the pushing and which object is being pushed
- 6. Force Arrow Pull of magnet on nail The magnet is pulling and the nail is being pulled Exercise: Draw the force arrow of push of wall on ladder.
- 7. Force Can Make Things Move Force can make things move. You have to push a shopping trolley to start it moving around the shop. You have to pull on a handle to open a drawer.
- 8. Measuring Forces Forcemeter (Newtonmeter) is an instrument to measure force. See your textbook (stage 7) page 131 for the clearer picture of forcemeter
- 9. How a Forcemeter Works ? There is a spring inside a forcemeter. The pulling force stretches the spring and this moves the indicator along the scale. The bigger the force, the further the indicator moves.
- 10. The Unit of Force The unit of force is newtons (N). The unit is named after Isaac Newton, an English Scientist who explained how forces affect the way things move. Answer the question from the textbook (stage 7) page 132
- 11. Weight The Pull of Gravity We live on the earth. Its difficult to get away from the earth. If you jump upwards, you fall back down again. The earths gravity pulls you downwards. The earths gravity causes a force that pulls any object downwards. The force is called weight. Like any other force, weight is measured in newtons (N). Gravity always pulls you towards the centre of the earth. It doesnt matter where you are on the surface of the earth.
- 12. Weight The Pull of Gravity An objects weight is a force acting towards the centre of the earth
- 13. Weight The Pull of Gravity Our weight is caused by the pull of the earths gravity. It pulls you downwards All object has weight
- 14. Falling Through The Floor The earths gravity is pulling on us all the time. It pulls us downwards, but we dont fall through the floor. Why not ? The floor pushes upwards on us with a force. This force is called contact force. Any object that you push on pushes back with a contact force.
- 15. Contact Force
- 16. Contact Force Usually the force is big enough to balance the pull of gravity. But if you stand on something that isnt very strong, its upward push may not be enough to support you.
- 17. Mass and Weight W = m x g W is weight (N) m is mass (kg) g is earths gravity constant (10 m/s2 ) Mass is the amount of matter in an object, measured in kg. Weight is the force of gravity on an object, measured in N.
- 18. Exercise Answer the question from textbook (stage 7) page 132. The mass of object is 50 kg, what is the weight of object on earth ? 5 apples have weight of 5 N. What is the mass of 5 apples on earth ?
- 19. The Moons Gravity The moons gravity is weaker than the Earths. You weigh a lot less up there. You can jump much higher on the Moon but you still fall back downwards. If you go far out into space, far from the earth, moon or any other object, your weight is zero. Your mass stays the same, however you are still made of 50 kg of matter, for example.
- 20. The Moons Gravity Moons gravity and earths gravity are different. Earths gravity and other planets gravity are different. Answer the question from textbook (stage 7) page 135.
- 21. Friction Rubbing your hands together. The force of friction causes them to warm up. Friction is a force that acts when two surfaces are in contact with each other
- 22. Friction If you try to push it to the right, the force of friction pushes back in the opposite direction to the left. The force of friction makes it difficult to move a heavy object. Eventually, if you push hard enough, the box will move. Your pushing force is greater than the force of friction.
- 23. Friction Friction acts to oppose motion
- 24. Friction The car is pushed to the right. Mention all forces on the car.
- 25. Friction A man is playing ski on the snow. Can you mention all forces on the man ?
- 26. Exercise Mention all forces on the box.
- 27. Investigating Friction Add weigh on top of the block to make it heavier. Turn the block so that a different face is in contact with the bench. This changes the area of contact. Use a material such as paper or cling film to cover the surface, make it rougher or smoother. See your textbook (stage 7) page 137, Activity 9.4
- 29. Air Resistance If you drop something, it falls to the ground. Its weight the pull of the Earths Gravity makes it fall. Air resistance : Force that acts on any object moving through the air
- 30. Air Resistance The parachutists will not be travelling very fast when they hit the ground. This is because they are falling through the air. This means that there is another force acting on them. This extra force is the force of air resistance. The force of air resistance slows them down to a safe speed.
- 31. Air Resistance Air resistance and weight are equal in size but point in opposite directions, so they can cancel each other out. When forces cancel each other out like this, we say that the forces are balanced. Air is very thin substance, so we can move easily through it. Thats why a parachute must have such a big area. A small parachute will be useless.
- 32. Air Resistance The flying squirrel uses air resistance to help it glides through the air
- 33. Air Resistance and Friction Air resistance is like friction. It tends to slow down anything that is moving. A large area gives a lot of air resistance. The aircraft in the photograph is designed to move easily through the air. A shape like this is described as streamlined. Streamlined shape reduces air resistance.
- 34. Thrust : A type of force (usually in a car or plane) that pushes the vehicle forwards Upthrust : The force on an object in a liquid or gas that pushes it up For example : if an object is floating, the water is pushing it up ; Balloons also experience this force because the air below the balloons pushes it up If you pull something with a rope/wire/cable/piece of string that has a weight on it, there is a force called TENSION Electrostatic Force The force acts between object that are charged (have a positive or negative) It can attract or repel (push away)
- 35. Balanced and Unbalanced Forces Balanced Forces If the forces are the same size but in opposite direction (equal) The object behaves as if theres no force acting on it If your object is moving but with a constant/steady speed Unbalanced Forces If the forces on an object are not equal
- 36. Resultant Forces Resultant Force : The Single Force equivalent to two or more forces acting on an object
- 37. End of Chapter Answer all questions from textbook (stage 7) page 142 143