Forces -Review- IS3

What can you infer from the image? Suppose you observe a proton moving through a region of outer space, far from almost all other objects. The proton moves along a path like the one shown on the left. The arrow indicates the initial direction of the proton’s motion, and the “x’s” in the diagram indicate the position of the proton at equal time intervals. Do you see evidence that the proton is interacting with another object?

What keeps the atom’s particles together?

Describe the motion

What forces are acting on you?

What forces are acting on the cart?

What is Force? Force is an interaction that causes a change in motion Described by vectors Vectors have magnitude and direction Unit: Newton (N) 1N: force required to give a 1kg object an acceleration of 1m/s2 Contact forces: friction, normal, air resistance Non-contact forces: gravity, magnetism, electrical force

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

Determining the net force… Net force: vector sum of all the forces that act upon an object

Balanced or Unbalanced?

What forces are acting on the football in the air?

Friction Force that 2 materials exert on each other Causes: type of surface involved + how hard surfaces push together Acts in a direction opposite to the direction of the object’s motion It depends on an object’s mass

Draw the free-body diagrams… 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.  An egg is free-falling from a nest in a tree. Neglect air resistance. Diagram the forces acting on the egg as it is falling. 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 rightward force is applied to a book in order to move it across a desk with a rightward acceleration. Consider frictional forces. Neglect air resistance. Diagram the forces acting on the book. 

Gravity Attraction between all matter Downward force of gravity on an object is called weight Earth: acceleration due to gravity = 9.8m/s2 Force: mass x acceleration (F=ma  W=ma) Newton realized it is universal (Law of Universal Gravitation) Factors affecting: mass and distance

Mass x Weight: Mass: amount of matter => measure of body’s inertia Weight: effect of gravity on mass  Force = mass x acceleration  Weight = mass x acceleration Example 1: Earth Weight = 50Kg x 9.8m/s2 Weight = 490 kg . m = 490N s2 Example 2: Jupiter Weight = 50Kg x 24.8m/s2 Weight = 1240 kg . m = 1240N

Moon: Apollo 15

NEWTON’S LAWS The Three Laws of Motion by Sir Isaac Newton explain all aspects of motion.

Galileo’s experiment

Newton's First Law: “An object at rest will remain at rest, and a moving object will remain at a constant speed unless unbalanced forces act on it”. Inertia: ability to resist change in motion Egg drop inertia

Newton's Second Law: “An object that has an unbalanced force acting on it will accelerate in the direction of the force”. · Force = mass X acceleration (F = ma) · change in motion proportional to force applied, inversely proportional to body’s mass

Newton's Third Law: “For every action, there is an equal and opposite reaction” Forces act in pairs Mission to Mars movie

Exit Card Relate each Simpsons video with one Law of Motion and explain. Use the words associated with the specific law in your answer a) Krusty is driving a car, the car hits a tree and Krusty is ejected from the car through the windshield while the car stops.   b) Bart is inside a warehouse. He finds a chair with wheels and a fire extinguisher. He decides to sit on the chair and pull the fire extinguisher’s handle. Air comes out of it. Bart’s chair moves to the back of the room.