Transcript Motion
Motion Motion Motion is a change in position Frame of Reference A place or object that is fixed (not moving) Ex: A bus is driving by. Your reference is trees on the other side of the bus. This shows the bus is moving relative to the trees. If you are in the bus and your reference is the other kids on the bus the kids do not appear to be moving. Speed How fast something is going Speed=Distance/Time Ex: If I walk 6m and it takes 3s, what is my speed? Speed=Distance/Time Speed=6m/3s Speed=2m/s Constant Speed A moving object that does not chnge its speed On a distance time graph this would be a strait line. Average Speed Total Distance/Total Time Average speed is important because most cars do not move at a constant speed during its entire ride. Velocity Speed Ex: in a particular direction A car with a speed of 10m/s and heading north would have a velocity of 10m/s northwards Velocity Cont. Velocity is a vector represented by an arrow. The length of the arrow represents speed and the way the arrow points represents direction Acceleration Change in speed and/or direction Acceleration = Velocity/Time Speeding up=Positive acceleration Slowing Down=Negative acceleration Ex: When a car slows down you move forward, and when a car speeds up you are pushed back into the seat. Acceleration Cont. Newton’s First Law An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force. Newton’s First Law Also called law of inertia Inertia is the tendency of an object to resist change in its motion. Ex: When you break in a car suddenly. Your body keeps moving forward because of inertia. https://www.youtube.com/watch?v=yZM EUT-Ipv4 Balanced/Unbalanced Forces Balanced Forces – 2 forces are acting in opposite directions with the same amount of force. The net force would be 0 and this object would not move. Unbalanced forces – 2 forces are acting in the same direction, or in opposite directions with different amounts of force. The net force would not be 0, and this object would move in the direction of the larger force. Net Force The end result of the forces added together (when acting upon an object in the same direction) or subtracted from one another (when acting upon an object in opposite directions) If net force = 0 the object is not moving If net force ≠ 0 the object will move in direction of larger force Newton’s First Law Let’s think about a book on a table. Once force acting upon the book is gravity pulling it toward the ground A second force is the table pushing back on the book. These forces are acting in opposite directions with the same force so the book is balanced or not moving Newton’s First Law Cont. When a book is being slid across the table there are 4 forces acting upon the book. The table and gravity are equal so the book does not move up or down. The push of the book acts in one direction and friction acts in the opposite direction The push is a bigger force, so it causes the book to move because that force is bigger than the friction working against it. Newton’s First Law Cont. Newton’s 1st law is sometimes called the law of inertia Inertia – the tendency of all objects to resist any change in motion Objects with smaller mass have smaller inertia. This is why it is easier to push and stop a bike than a car. Newton’s Second Law of Motion The acceleration of an object depends on the mass of the object and the amount of force applied. Greater force = More acceleration Greater mass = Less acceleration All objects fall to the ground with the same acceleration (9.8 m/s²) Newton’s Third Law Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first. https://www.youtube.com/watch?v=mFN e_pFZrsA Ex: You sitting on a chair. The force of gravity pulling you down is equal to the force of the chair pushing up on you. Ex: dropping a ball. The force of gravity is pulling the ball toward the ground and the ground toward the ball Newton’s third Law Cont. Unbalanced forces result in movement because the action and reaction act on 2 different objects. Ex: Kangaroo Jumping Action: Kangaroo on ground, Reaction: ground on Kangaroo Results in the kangaroo jumping Law of conservation of Energy https://www.youtube.com/watch?v=8GLt FNaiMH8