Key Concepts What is Newton’s first law of motion? What is Newton’s second law of motion? Key Terms - Inertia

 An object at rest will remain at rest, and an object moving at a constant velocity will continue moving at a constant velocity, unless acted upon by an unbalanced force  Clothes on the floor will stay there unless someone uses a force to pick them up  A tennis ball that was hit will continue until a force stops it  Gravity and friction are the 2 forces on Earth that often change an object’s motion

 Tendency of an object to resist a change in motion  Newton’s first law is also called the Law of Inertia  Example – a person continues to move forward when a car stops

 The greater the mass of an object, the greater the inertia  The greater the inertia, the greater the force needed to move the object, and the greater the force needed to change its motion

 Acceleration depends on the object’s mass and the net force acting on the object  Acceleration = Net Force Mass  Force = mass * acceleration Units = Newton (N) = kg *m/s 2

 Calculating Force: A speedboat pulls a 55kg water skier. The force causes the skier to accelerate at 2.0m/s 2. Calculate the net force that causes this acceleration.  Information given: ◦ Mass of water skier =55kg ◦ Acceleration of water skier= 2.0 m/s 2  What quantity are you trying to calculate? ◦ Net force F net  What formula should you use?  A = f net or F net = m*a m  Perform calculation – 55kg *2.0m/s 2 = 110kg*m/s 2 = 110N

 What is the net force on a 1,000 kg object accelerating at 3 m/s 2 ?

 What net force is needed to accelerate a 25 kg cart at 14m/s 2 ?

 If you keep the mass constant, a change in force will have the same change in the acceleration  If you keep the force constant, an increase in mass will cause a decrease in acceleration  Opposite is also true – If the force is constant, a decrease in mass will cause an increase in acceleration

 tlaws/u2l1b.cfm tlaws/u2l1b.cfm  alSci_1stSem.htm alSci_1stSem.htm