2. Scope of the presentation Scope of this presentation is to learn below engineering concepts : Gravity Weight Mass Force Note : All the above engineering concepts are interlinked with each other.

3. Gravity Newton was the first person to seriously study gravity Gravity is a force that attracts all objects toward each other. The force of gravity is measured in units called Newtons (N ).

4. Gravity The strength of gravity between two objects depends on two factors: 1. Masses of the objects (If mass increases, force also increases) 2. Distance between the objects (If distance increases, force decreases)

5. Gravity force The greater the mass, the greater the force distanceless The greater the distance, the less the force Acceleration due to gravity = 9.8 m/s/s or 9.8 m/s 2

6. Mass and weight

7. Mass Vs Weight MASS WEIGHT Is the amount of matter in an object is the force of gravity on an object Always remains constant Weight of an object changes if the gravity changes Does not depend on gravityWeight=mass X Gravity

8. Measuring unit for Mass Mass is measured in grams and kilograms. 1 paper clip= 1 gram 1000g=1 kilogram

10. Force A force is a push or a pull. Force gives an object the energy to move, stop moving, or change direction. When you write with a pen you exert a force. When you peddle your bike, blow your nose, chew your gum, or swimming in a pool, you are exerting forces on other objects. We would never be able to move without exerting forces on things

11. Newtons 2nd Law: Fnet = m a The acceleration an object undergoes is directly proportion to the net force acting on it. Mass is the constant of proportionality. For a given mass, if F net doubles, triples, etc. in size, so does a. For a given F net if m doubles, a is cut in half. F net and a are vectors; m is a scalar. F net and a always point in the same direction. The 1 st law is really a special case of the 2 nd law (if net force is zero, so is acceleration).

12. What is Net Force? When more than one force acts on a body, the net force (resultant force) is the vector combination of all the forces, i.e., the “net effect.” F1F1 F2F2 F3F3 F net

13. Net Force & the 2nd Law For a while, we’ll only deal with forces that are horizontal or vertical. When forces act in the same line, we can just add or subtract their magnitudes to find the net force. 2 kg 15 N 32 N F net = 27 N to the right a = 13.5 m/s 2 10 N

14. Normal force directions Up You’re standing on level ground. Sideways A ladder leans up against a wall. At an angle A race car takes a turn on a banked track. Down You’re in a roller coaster at the top of a loop.

15. Find out the forces? Weight (N) Reaction Force (N)

16. Answer for Question 1 1) The first force is weight, and weight always acts from the centre of the object. (strictly it acts from the centre of mass, for example a lollipop’s weight would be labelled approximately at the centre of the sweet, rather than the centre of the stick, because the sweet is heavier than the stick) 2) Reaction force acts at 90 degrees to the surface at the point of contact between the surface and the object. Therefore it is drawn acting from the floor upwards, at the middle of the cat.

17. Find out the forces? Weight (N) Reaction Force (N) Friction (N)

18. Answer for Question 2 The reaction force always acts at 90 degrees to the slope of the surface at the point where the cat and roof meet. Weight always acts down. Friction acts parallel to the surface, at the point of contact between the object and the surface.

19. Find out the forces? Weight (N) Reaction Forces (N) Friction (N)

20. Answer for Question 3 This reinforces the ‘reaction force is at 90 degrees to the surface at the point of contact’ as there are many points of contact.

21. Find out the forces on WHEELBARROW ? Weight (N) Reaction Force (N) Friction (N) Lifting Force (N)

22. Answer for Question 4 1) Weight acts from the centre of the wheelbarrow 2) Reaction Force acts from the point of contact between the wheel and the ground, at 90 degrees to the ground. 3) Friction acts parallel to the surface, at the point of contact between the object and the surface.

23. Find out the forces? Weight (N) Upthrust (N) Drag (N) Wind Force (N)

24. Answer for Question 5 1) Weight acts down form the centre of the boat 2) Upthrust acts like reaction force, except is the equivalent for water. 3) Wind force pushes on the centre of the sail 4) Drag acts like friction, except for water. It opposes the direction of motion, and occurs in water and air. Imagine riding a motorbike on a still day, not even a breeze. When you speed up, you feel a wind against your face. This is the air pushing you back, and is called drag. The same happens in water.

25. Find out the forces? Weight (N) Reaction Force (N) Drag (N) Driving Force (N)

26. Answer for Question 6 1) Weight, acting downwards from the centre 2) Reaction force, acting upwards at the wheels 3) Driving force, forwards direction - simply showing this force is forwards is sufficient. See notes below for further details on this force. 4) Drag – opposes motion

27. Find out the forces? Weight (N) Reaction Force (N) Force (N)

28. Answer for Question 7 1) Weight, from centre downwards 2) Reaction, from ground upwards 3) Wind and rain forces