Newtons Law 2 F ma Intro thoughts Newtons

Newton’s Law #2 – ∑F = ma

Intro thoughts… Newton's first law of motion predicts the behaviour of objects for which all existing forces are balanced. If the forces acting upon an object are balanced, then the acceleration of that object will be…

Intro thoughts… Newton's first law of motion predicts the behaviour of objects for which all existing forces are balanced. If the forces acting upon an object are balanced, then the acceleration of that object will be 0 m/s/s. In other words, the object will not…

Intro thoughts… Newton's first law of motion predicts the behaviour of objects for which all existing forces are balanced. If the forces acting upon an object are balanced, then the acceleration of that object will be 0 m/s/s. In other words, the object will not change its speed or direction.

Intro thoughts… Newton's second law of motion pertains to the behaviour of objects for which all existing forces are not balanced. The second law states that the acceleration of an object is dependent upon two variables…can you guess what they are?

Activity http: //www. physicsclassroom. com/Physics-Interactives/Newtons. Laws/Force-Interactive

Scenario #1 500 N Weight = 1000 N Which object accelerates more? 500 N Weight = 1500 N

Scenario #2 500 N Weight = 1000 N Which object accelerates more? 600 N Weight = 1000 N

Intro thoughts… The acceleration of an object is dependent upon… n Mass of object n Size of force applied

Newton’s Second Law Unbalanced forces cause objects to accelerate with an acceleration that is directly proportional to the net force and inversely proportional to the mass. Can you write this as an equation? ?

Newton’s Second Law

Thinking time…

Quick practice questions… Net Force ( ) Mass ( 10 2 20 4 2 10 ) Acceleration ( 5 10 )

Quick practice questions… Net Force (N) Mass (kg) Acceleration (m/s/s) 10 2 5 20 4 5 10 2 5 10 1 10

Scenario: medicine ball v. basketball Fill in the following table with your predictions: MEDICINE BALL MASS WEIGHT FORCE OF GRAVITY ACCELERATION DUE TO GRAVITY AIR RESISTANCE HIT THE GROUND BASKETBALL

Let’s have a look… https: //www. youtube. com/watch? v=o. Bdalz. RJR 5 g&

Scenario: medicine ball v. basketball Fill in the following table with your predictions: MEDICINE BALL BASKETBALL MASS MORE LESS WEIGHT MORE LESS FORCE OF GRAVITY ? ? ACCELERATION DUE TO GRAVITY ? ? AIR RESISTANCE SAME HIT THE GROUND SAME

Scenario: medicine ball v. basketball Fill in the following table with your predictions: MEDICINE BALL BASKETBALL MASS MORE LESS WEIGHT MORE LESS FORCE OF GRAVITY ? ? ACCELERATION DUE TO GRAVITY SAME AIR RESISTANCE SAME HIT THE GROUND SAME

Free-Body Diagrams Free-body diagrams are diagrams used to show the relative magnitude and direction of all forces acting upon an object in a given situation

Free-Body Diagrams The _ _of the arrow in a free-body diagram reflects the magnitude of the force. The direction of the arrow shows the _ _ _ _ _ that the force is acting.

Free-Body Diagrams Question: Will you always have to draw four forces in a free-body diagram?

Practice Questions A book is at rest on a tabletop. Diagram the forces acting on the book. A girl is suspended motionless from the ceiling by two ropes. Diagram the forces acting on the combination of girl and bar. A flying squirrel is gliding (no wing flaps) from a tree to the ground at constant velocity. Consider air resistance. Diagram the forces acting on the squirrel. A car is coasting to the right and slowing down. Neglect air resistance. Diagram the forces acting upon the car.

Go to the following link and complete the activities http: //www. physicsclassroom. com/Physics. Interactives/Newtons-Laws/Free-Body-Diagrams

Scenario: medicine ball v. basketball So…what’s happening here? MEDICINE BALL BASKETBALL MASS MORE LESS WEIGHT MORE LESS FORCE OF GRAVITY ? ? ACCELERATION DUE TO GRAVITY ? ? AIR RESISTANCE SAME HIT THE GROUND SAME

http: //www. physicsclassroom. com/mmedia/newtlaw s/efff. cfm http: //www. physicsclassroom. com/mmedia/newtlaw s/efar. cfm

True or False? 1. The elephant and the feather each have the same force of gravity. 2. The elephant has more mass, yet both elephant and feather experience the same 3. 4. 5. 6. 7. 8. force of gravity. The elephant experiences a greater force of gravity, yet both the elephant and the feather have the same mass. On earth, all objects (whether an elephant or a feather) have the same force of gravity. The elephant weighs more than the feather, yet they each have the same mass. The elephant clearly has more mass than the feather, yet they each weigh the same. The elephant clearly has more mass than the feather, yet the amount of gravity (force) is the same for each. The elephant has the greatest acceleration, yet the amount of gravity is the same for each.

True or False? 1. The elephant encounters a smaller force of air resistance than the feather and 2. 3. 4. 5. 6. 7. 8. therefore falls faster. The elephant has a greater acceleration of gravity than the feather and therefore falls faster. Both elephant and feather have the same force of gravity, yet the acceleration of gravity is greatest for the elephant. Both elephant and feather have the same force of gravity, yet the feather experiences a greater air resistance. Each object experiences the same amount of air resistance, yet the elephant experiences the greatest force of gravity. Each object experiences the same amount of air resistance, yet the feather experiences the greatest force of gravity. The feather weighs more than the elephant, and therefore will not accelerate as rapidly as the elephant. Both elephant and feather weigh the same amount, yet the greater mass of the feather leads to a smaller acceleration.

Task: Complete the following qs 8. 2 Unit Review (p 292) n 1, 3, 4, 7, 8, 11, 14, 15