Newton’s First & Second Laws of Motion Chp 12.2 Pg

Newton’s First Law of Motion  According to the 1st Law of motion, the state of motion of an object does not change as long as the net force on the object is zero  Unless an unbalanced force acts, an object at rest will remain at rest and an object in motion will remain in motion at constant velocity  According to the 1st Law of motion, the state of motion of an object does not change as long as the net force on the object is zero  Unless an unbalanced force acts, an object at rest will remain at rest and an object in motion will remain in motion at constant velocity

Inertia  Newton’s 1st Law is known as the Law of Inertia  Inertia is the tendency of an object to resist change in its motion.  An object at rest stays at rest and an object in motion stays in motion at constant velocity  Newton’s 1st Law is known as the Law of Inertia  Inertia is the tendency of an object to resist change in its motion.  An object at rest stays at rest and an object in motion stays in motion at constant velocity The coin stays in place above the cup, then falls The coin wants to stay at rest

Inertia continued The man wants to stay in motion. So he continues moving forward at constant velocity. However, gravity begins to act on him while he is airborne and eventually he will fall to the ground

Inertia and Car Accidents Wear your seatbelt!!!!! Head keeps moving

Newton’s Second Law  Mass is a measure of the inertia of an object that depends on the amount of matter the object contains. (an amount of matter)  Acceleration of an object is equal to the net force acting on it divided by the object’s mass  Mass is a measure of the inertia of an object that depends on the amount of matter the object contains. (an amount of matter)  Acceleration of an object is equal to the net force acting on it divided by the object’s mass

2nd Law Formula variations and units  Force = mass x acceleration  F = m x a units = Kg x m/s 2 = Kgm/s 2 = N  Acceleration = Net force Mass  a = _F_ units = N or Kgm/s 2 = m/s 2 m Kg Kg  Mass = force acceleration  M = F units = N or Kgm/s 2 = Kg a m/s 2 m/s 2  Force = mass x acceleration  F = m x a units = Kg x m/s 2 = Kgm/s 2 = N  Acceleration = Net force Mass  a = _F_ units = N or Kgm/s 2 = m/s 2 m Kg Kg  Mass = force acceleration  M = F units = N or Kgm/s 2 = Kg a m/s 2 m/s 2

A car with a mass of 1200 kg accelerates at a rate of 2 m/s 2 in the forward direction. What is the net force acting on the car?  Given info: m = 1200 kg a = 2 m/s 2 Step 1 Step 2 Step 3 F = m x a F = 1200 kg x 2 m/s 2 F = 2400 kgm/s 2 or 2400 N  Given info: m = 1200 kg a = 2 m/s 2 Step 1 Step 2 Step 3 F = m x a F = 1200 kg x 2 m/s 2 F = 2400 kgm/s 2 or 2400 N

 Given info: m = 1000 kg F = 2000N Step 1 Step 2 Step 3 a = F a = 2000 N kgm/s 2 a = 2 m/s 2 m 1000 kg  Given info: m = 1000 kg F = 2000N Step 1 Step 2 Step 3 a = F a = 2000 N kgm/s 2 a = 2 m/s 2 m 1000 kg A car with a mass of 1000 kg accelerates when the light turns green. If the net force on the car is 2000 N what is the car’s acceleration?

A 30 N force accelerates a boy on a skateboard at 0.5 m/s 2. What is the mass of the boy and skateboard?  Given info: a = 0.5 m/s 2 F = 30 N Step 1 Step 2 Step 3 m = F m = 30 N kgm/s 2 m = 60 kg a 0.5 m/s s  Given info: a = 0.5 m/s 2 F = 30 N Step 1 Step 2 Step 3 m = F m = 30 N kgm/s 2 m = 60 kg a 0.5 m/s s

Weight and Mass  Weight is the force of gravity acting on an object. It is the product of the object’s mass and acceleration due to gravity acting on it.  Mass and weight are not the same. The unit for mass is kg and unit for weight is N  Mass is the measure of inertia on an object (an amount of matter); weight is a measure of the force of gravity acting on an object  Weight is the force of gravity acting on an object. It is the product of the object’s mass and acceleration due to gravity acting on it.  Mass and weight are not the same. The unit for mass is kg and unit for weight is N  Mass is the measure of inertia on an object (an amount of matter); weight is a measure of the force of gravity acting on an object

Weight problems  Weight = mass x acceleration due to gravity  w = m x g  Units = kg x m/s 2 = kgm/s 2 = N  What is the weight of a man if his mass is 112 kg and gravity is 9.8m/s 2 ? w = m x g w = 112 kg x 9.8 m/s 2 w = 1100 kgm/s 2 or 1100N  Weight = mass x acceleration due to gravity  w = m x g  Units = kg x m/s 2 = kgm/s 2 = N  What is the weight of a man if his mass is 112 kg and gravity is 9.8m/s 2 ? w = m x g w = 112 kg x 9.8 m/s 2 w = 1100 kgm/s 2 or 1100N

Weight changes if gravity changes  If gravity the moon is 1/6 that of Earth’s gravity the weight of a 60 N rock on Earth will only be 10 N on the moon.  What would the weight of a dog be on the moon if its weight on earth is 54 N?  54 N x 1 = 9 N 6  No matter the gravity, mass is always the same  If gravity the moon is 1/6 that of Earth’s gravity the weight of a 60 N rock on Earth will only be 10 N on the moon.  What would the weight of a dog be on the moon if its weight on earth is 54 N?  54 N x 1 = 9 N 6  No matter the gravity, mass is always the same