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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 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
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…1. A book is at rest on a tabletop. Diagram the forces acting on the book. 2. A girl is suspended motionless from the ceiling by two ropes. Diagram the forces acting on the combination of girl and bar. 3. 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.4. 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. 5. 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 accelerationExample 1: Earth Weight = 50Kg x 9.8m/s2 Weight = 490 kg . m = 490N s2Example 2: Jupiter Weight = 50Kg x 24.8m/s2 Weight = 1240 kg . m = 1240N s2
Newtons 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
Newtons 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
Newtons Third Law:• “For every action, there is an equal and opposite reaction”• Forces act in pairs• Mission to Mars movie
Exit CardRelate each Simpsons video with one Law of Motion and explain. Use the words associated with the specific law in your answera) 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.