# Newton’s Second Law Coach Dave Edinger J. C. Booth Middle School Physical Science (8A) Mrs. Coach Ed R-O-C-K-S !!!

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Newton’s Second Law Coach Dave Edinger J. C. Booth Middle School Physical Science (8A) Mrs. Coach Ed R-O-C-K-S !!!

Newton’s 1st law REVIEW Summarize what the law states. What does an object at rest need for it to move? What is another name for Newton’s first law of motion? What is inertia? What causes a moving object to stop moving? The (more/less) mass an object has, the harder it is to move. The (more/less) mass an object has, the easier it is to move.

NEWTON’S second law The acceleration of an object depends on the mass of the object and the amount of force applied. VOLUNTEERS!!!!! TWO “pushers” of similar size ONE small 8 th grader ONE big 8 th grader

Part 1: Acceleration depends on mass Acceleration of an object decreases as its mass increases. Acceleration of an object increases as its mass decreases. Which would be easier to push? WHY?

Part 2: Acceleration depends on force Acceleration of an object increases as the force on it increases Acceleration of an object decreases as the force on it decreases VOLUNTEERS!!!!! ONE to sit in chair ONE to push chair

Newton’s law with MATH Formula: Force = mass acceleration UNITS  m/s² accleration: m/s² (meters per second squared) N force: N (Newtons) kg mass: kg ( kilograms) F ma

Tricky…tricky…. You don’t use Newtons to find acceleration in this formula 1 N = 1 kg∙m/s² 4 N = 4 kg∙m/s² So…4 N = 4 kg∙m/s² 500 N = 500 kg∙m/s² And….500 N = 500 kg∙m/s² 395 N = ? And 395 N = ?

Newton and math example Mass of apple: 0.102kg Force: 1 N What is the acceleration?

Newton and math example Mass of apple: 0.102kg Force: 1 N What is the acceleration? a = F/m

Newton and math example Mass of apple: 0.102kg Force: 1 N What is the acceleration? a = F/m a = 1N / 0.102kg

Newton and math example Mass of apple: 0.102kg Force: 1 N What is the acceleration? a = F/m a = 1N / 0.102kg a= 1 kg∙m/s² / 0.102kg a= 9.8 m/s 2

Practice What is the acceleration of a 7kg mass if a force of 68.6 N is used to move the mass? a = F / m

Practice What is the acceleration of a 7kg mass if a force of 68.6 N is used to move it toward earth? a = F / m N a = 68.6 N / 7 kg

Practice What is the acceleration of a 7kg mass if a force of 68.6 N is used to move it toward earth? a = F / m N a = 68.6 N / 7 kg kg m/s 2 a = 68.6 kg m/s 2 / 7 kg

Practice What is the acceleration of a 7kg mass if a force of 68.6 N is used to move it toward earth? a = F / m N a = 68.6 N / 7 kg kg m/s 2 a = 68.6 kg m/s 2 / 7 kg a = 9.8 m/s 2

Practice What is the acceleration of a 7kg mass if a force of 68.6 N is used to move it toward earth? a = F / m N a = 68.6 N / 7 kg kg m/s 2 a = 68.6 kg m/s 2 / 7 kg a = 9.8 m/s 2

Practice What is the acceleration of a 7kg mass if a force of 68.6 N is used to move it toward earth? a = F / m N a = 68.6 N / 7 kg kg m/s 2 a = 68.6 kg m/s 2 / 7 kg a = 9.8 m/s 2

Challenge question What force is necessary to accelerate a 1,250kg car at a rate of 40 m/s² ?

Challenge question What force is necessary to accelerate a 1,250kg car at a rate of 40 m/s² ? F = ma

Challenge question What force is necessary to accelerate a 1,250kg car at a rate of 40 m/s² ? F = ma F = 1250 kg 40 m/s 2

Challenge question What force is necessary to accelerate a 1,250kg car at a rate of 40 m/s² ? F = ma F = 1250 kg 40 m/s 2 kg m/s 2 F = 50,000 kg m/s 2

Challenge question What force is necessary to accelerate a 1,250kg car at a rate of 40 m/s² ? F = ma F = 1250 kg 40 m/s 2 kg m/s 2 F = 50,000 kg m/s 2 F = 50,000 N

Another challenging question Zookeepers carry a stretcher that holds a sleeping lion. The total mass of the lion and the stretcher is 175 kg. The lion’s forward acceleration is 2 m/s². What is the force necessary to produce this acceleration?

Another challenging question Zookeepers carry a stretcher that holds a sleeping lion. The total mass of the lion and the stretcher is 175 kg. The lion’s forward acceleration is 2 m/s². What is the force necessary to produce this acceleration? F = ma

Another challenging question Zookeepers carry a stretcher that holds a sleeping lion. The total mass of the lion and the stretcher is 175 kg. The lion’s forward acceleration is 2 m/s². What is the force necessary to produce this acceleration? F = ma F = 175 kg 2 m/s 2

Another challenging question Zookeepers carry a stretcher that holds a sleeping lion. The total mass of the lion and the stretcher is 175 kg. The lion’s forward acceleration is 2 m/s². What is the force necessary to produce this acceleration? F = ma F = 175 kg 2 m/s 2 kg m/s 2 F = 350 kg m/s 2

Another challenging question Zookeepers carry a stretcher that holds a sleeping lion. The total mass of the lion and the stretcher is 175 kg. The lion’s forward acceleration is 2 m/s². What is the force necessary to produce this acceleration? F = ma F = 175 kg 2 m/s 2 kg m/s 2 F = 350 kg m/s 2 F = 350 N

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