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- 2. Definition
- 3. 2.1.1 What is inertia? 2.1.2 Relation between inertia and mass 2.1.3 Situation involving inertia 2.1.4 Ways to reduce negative effects of inertia
- 4. INERTIA <ul><li>The inertia of an object is the tendency of the object to remain at rest or if moving, to continue its motion in a straight line. </li></ul>Newton’s first law of motion Newton;s first law states that, “Every object continues in its state of rest or uniform motion unless it is acted upon by an external force.”
- 5. <ul><li>When both pail are pushed, it is found that the empty bucket is easier to push compared to the bucket with sand. </li></ul><ul><li>When both buckets are oscillating and an attempt is made to stop them, the bucket filled with sand is more difficult to stop. </li></ul><ul><li>An object with a larger mass has a larger inertia. </li></ul>Relation between inertia and mass “ The larger the mass, the larger the inertia”
- 6. SITUATIONS INVOLVING INERTIA SITUATION EXPLANATION <ul><li>When the cardboard is pulled away quickly, the coin drops straight into the glass. </li></ul><ul><li>The inertia of the coin maintains its state at rest . </li></ul><ul><li>The coin falls into the glass due to gravity. </li></ul><ul><li>The sauce inside the bottle moves together with the bottle. </li></ul><ul><li>When the bottle stops suddenly, the sauce continues in its state of motion due to the effect of its inertia . </li></ul>
- 7. SITUATION EXPLANATION <ul><li>Body moves forward when the car stops suddenly . </li></ul><ul><li>The passengers were in a state of motion when the car was moving. </li></ul><ul><li>When the car stopped suddenly, the inertia in the passengers made them maintain their state of motion . </li></ul><ul><li>Thus when the car stops, the passengers moved forward. </li></ul><ul><li>A boy runs away from a cow in a zig zag motion. </li></ul><ul><li>The cow has a large inertia making it difficult to change direction. </li></ul>
- 8. <ul><li>Furniture carried by a lorry normally are tied up together by string. </li></ul><ul><li>When the lorry starts to move suddenly, the furniture are more difficult to fall off due to their inertia because their combined mass has increased . </li></ul>Ways to Reduce Negative Effects of Inertia
- 9. Safety belt Prevent driver from thrown forward due to inertia. Safety Airbag To prevent the driver from hitting the steering wheel or dashboard during a collision.
- 11. m 1 =0.02 kg v 2 = 2ms -1 m 2 = 1000 kg m 1 = 1000 kg v 2 = 80 ms -1 v 1 = 100 ms -1 v 1 = 2ms -1 m 2 = 0.05 kg
- 12. MOMENTUM <ul><li>So if an object is moving, then it has momentum. </li></ul><ul><li>Momentum depends upon the variables mass and velocity . </li></ul><ul><li>Momentum is directly proportional to mass. </li></ul><ul><li>Momentum is directly proportional to the velocity. </li></ul>Is a product of mass and velocity Momentum, p = mass × velocity p = mv Unit: kgms -1 // Ns (vector quantity)
- 13. Principle of conservation of momentum states that in the absence of an external force, the total momentum of a system remains unchanged . PRINCIPLE OF CONSERVATION OF MOMENTUM
- 14. <ul><li>For a collision occurring between object 1 and object 2, the total momentum of the two objects before the collision is equal to the total momentum of the two objects after the collision . </li></ul>
- 15. <ul><li>Principle of conservation of momentum have 3 condition: </li></ul><ul><li>i) Elastic collision </li></ul><ul><li>ii) Inelastic collision </li></ul><ul><li>iii) Explosions </li></ul>
- 16. ELASTIC COLLISION INELASTIC COLLISION Both objects move independently at their respective velocities after the collision. The two objects combine and move together with a common velocity after the collision. Momentum is conserved Momentum is conserved.
- 17. ELASTIC COLLISION Total Momentum Before = Total momentum After m 1 u 1 + m 2 u 2 = m 1 v 1 + m 2 v 2
- 18. INELASTIC COLLISION Total Momentum Before = Total Momentum After m 1 u 1 + m 2 u 2 = (m 1 + m 2 ) v
- 19. EXPLOSIONS Before explosion both object stick together and at rest After collision , both object move at opposite direction .
- 20. EXPLOSION Total Momentum Before collision= Total Momentum After collision 0 = m 1 v 1 + m 2 v 2 m 1 v 1 = - m 2 v 2 negative sign means opposite direction
- 21. <ul><li>When a rifle is fired, the bullet of mass m, moves with a high velocity, v. This creates a momentum in the forward direction. </li></ul><ul><li>From the principle of conservation of momentum, an equal but opposite momentum is produced to recoil the riffle backward. </li></ul><ul><li>A high-speed hot gases are ejected from the back with high momentum. </li></ul><ul><li>This produces an equal and opposite momentum to propel the jet plane forward. </li></ul>
- 22. EXERCISE 1 <ul><li>Car A of mass 1000 kg moving at 20 ms -1 collides with a car B of mass 1200 kg moving at 10 ms -1 in same direction. If the car B is shunted forwards at 15 ms -1 by the impact, what is the velocity, v, of the car A immediately after the crash? [ans:14 ms -1 ] </li></ul>
- 23. EXERCISE 2 <ul><li>m A = 4 kg m B = 2 kg </li></ul><ul><li>u A = 10 m/s to the left </li></ul><ul><li>u B = 8 m/s to the right </li></ul><ul><li>v B = 4 m/s to the left. </li></ul><ul><li>Calculate the value of v A . [ans: 8m/s] </li></ul>A B A B
- 24. EXERCISE 3 <ul><li>A truck of mass 1200 kg moving at 30 m/s collides with a car of mass 1000 kg which is travelling in the opposite direction at 20 m/s. After the collision, the two vehicles move together. What is the velocity of both vehicles immediately after collision? [7.27 m/s] </li></ul>
- 25. EXERCISE 4 <ul><li>A man fires a pistol which has a mass of 1.5 kg. If the mass of the bullet is 10 g and it reaches a velocity of 300 m/s after shooting, what is the recoil velocity of the pistol? [ans: -2m/s] </li></ul>

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