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Transcript
Newton’s Second Law Newton’s First Law WarmUp 10-2-12 • What effect does extra mass have on the acceleration of an object if you don’t increase force 1.WarmUp 2. SCIVID 3. Newton’s 2nd Law science notes 4. Mini Vid on 2nd Law 5. Jumping Force Game WarmUp 10-22-12 • How does the gravitation force change as you go from picture A to picture B (when the mass decreases but distance stays the same)? A. Increases WarmUp SciVid 3rd Law Poster Bill Nye: Motion B. Decreases C. Stays the same D. Doesn’t change A B C Newton’s Second Law Newton’s Second Law Description Newton’s Second Law Math Short: Force= Mass x Acceleration Example: How much force will you need to use to push a pop machine that is 1000 kg with an acceleration of 2 meters per second per second Simple Rules: 1. The greater the force that is applied to an object the greater Acceleration it will have F= ma THE HARDER YOU PUSH THE MORE SOMETHING SPEEDS UP, SLOWS DOWN, OR CHANGES DIRECTION 2. If Force is unchanged, then the greater the Mass of an object the lower the acceleration will be THE HEAVIER SOMETHING IS THE HARDER IT IS TO MAKE SPEED UP, SLOW DOWN, CHANGE DIRECTION Draw a situation that describes the two rules Friction Friction: This is the force that always opposes motion. F = 1000 x 2= = 2000 N If we pushed a box of kleenex ( 2kg) with the same force ( 2000N) then what would our acceleration? HINT: If not solving for force, force is always on top F=ma A= F/m M=F/a A= F/M A= 2000 N/ 2 kg Three Types of Friction Static Friction: Friction between two surfaces that are not moving Rolling Friction: Friction between rolling object and a flat surface(least amount of friction Sliding Friction: Friction between flat surfaces where there is some movement but force must be constantly applied = 1000 m/s/s 3rd Law Poster Newton’s Third Law Short: Action/ Reaction Long: For every action force there is an equal and opposite reaction force Example: A NASA rocket shoots explosive gases into the ground… the group pushes back with the same force(based on mass and acceleration) and the rocket exits the earth More examples: 1. Breaking hand by punching someone in the face 2. Any propulsion device Person Mass (kg) Initial Force Mass= Weight/ 9.8 This is also the weight Final Force(Final F –Initial F) Jumping Force Jumping Acceleration (m/s/s) A= Force/Mass Mass x gravity Gravity Gravity: A force of attraction between two objects Weight: The effect of gravity on an object Weight = Mass x gravity Big objects attract little objects Time Speed (m/s) to them: The average skydiver hits his terminal velocity at a speed of 56 m/s When an object is in free fall it is no longer accelerating Acceleration Distance covered 1s 10 10 10 2s 20 10 30 30 10 60 4s 40 10 100 5s 50 10 150 6s 56 10 206 3s Terminal velocity: highest velocity a falling object can reach due to force air resistance = force gravity Mass ALL OBJECTS FALL AT THE SAME SPEED TOWARDS THE EARTH BUT SOME ARE AFFECTED MORE BY AIR. Why does a feather fall at a different speed than a hammer on earth but not on the moon? There is no air resistance on the moon! Belongs to an object( always the same) Weight Changes depending on the planet or moon Projectile Motion What if one object object is shot horizontally and another is dropped? The only force acting on either ball is GRAVITY so they fall at the same rate and hit the ground at the same time 1. At the same speed, which of the following has the greatest inertia? a. 1 kg b. 2 kg c. 5 kg d. 10 kg 2. What will happen to an object when a net force acts on it? a. Fall B. Stop C. Accelerate D. Go in a circle 3. According to Newton's 2nd law if you double the mass of an object and push with a constant force then the acceleration of that object will be a. b. c. d. halved unchanged doubled tripled 4. Two forces of 6 N and 3 N act upon an object in opposite directions. What is the net force acting on the object? (See image below) a. 3 N to the left b. 3 N to the right c. 9 N to the left d. 9 N to the right 5. A truck with a mass of 1000 kg hits a wall and unloads a force of 400,000 newtons. What is the negative acceleration of the trucks?. a. - 0.0025 m/s2 b. - 0.025 m/s2 c. - 40 m/s2 d. - 400 m/s2 WARMUP QUIZ 10-5-12