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Transcript
Newton’s First and Second Laws of Motion •How and why objects move as they do has fascinated scientists for thousands of years. •In the early 1600s, the Italian astronomer ___________________ suggested that, once an object is in motion, _____________ is needed to keep it ________________. •Force is needed only to ______________ the motion of an object. •Galileo's ideas paved the way for ___________________________. •Newton proposed the ____________________________________________ in the late 1600s. The First Law of Motion •Newton’s first law restates Galileo's ideas about ________________________. •Newton’s first law of motion states that ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ _____________________________. •If an object is _________ moving, it will _______________ until a ________ acts on it. •Clothes on the floor of your room will ________________ unless you pick them up. •If an object is _________________________, it will continue to move at a constant velocity until _____________________________ to change either its speed or direction. •For example, a tennis ball flies through the air once you hit is with a racket. •If your friend doesn’t hit the ball back, the forces of ___________________ _______________________ will eventually stop the ball. •On Earth, _______________________________ are unbalanced forces that often change an object’s motion. Inertia •Whether an object is moving or not, it _________________any change to its motion. •Galileo’s concept of the _______________ to a change in motion is called ________________. •Inertia is ____________________________________________________. •Newton’s first law of motion is called the ___________________________. •Inertia explains many common events, such as why you move _____________in your seat when a _________________________________. •When the car stops, inertia keeps you ___________________________. •A force, such as ___________________________________, it required to change your motion. •Some objects have _________________________ than other objects. •For example, suppose you needed to move an _______ aquarium and an aquarium _______________________. •Obviously, the full aquarium is harder to move than the empty one, because it has _________________________. •The ___________________________________ of an object, the _____________________, and the _______________________________ to change its motion. •The full aquarium is more difficult to move because it has __________________ than the empty aquarium. The Second Law of Motion •Suppose you are baby-sitting two children who love wagon rides. •Their favorite part is when you ___________________ quickly. •When you get tired and sit in the wagon, one of the children _______________. •He soon finds he _______________________________ the wagon nearly as fast as you can. •How is the wagon’s acceleration____________ to the ___________ pulling it? •How is the acceleration __________to the wagon’s __________? •According to Newton’s second law of motion____________________________ _____________________________________________________________ •This relationship can be written as an equation: ___________________________________________ •Acceleration is measured in meters per second per second ____________, and mass is measured in kilograms ___________. •According to Newton’s second law, then, force is measured in kilograms times meters per second per second _________________________________. •The short for this unit of force is the ___________________. •Recall that a newton is the metric unit of ______________. •You can think of one newton as the force required to give a 1-kg mass an acceleration of 1 m/s2. Sample Problem •A speedboat pulls a 55 kg water skier. The force causes the skier to accelerate at 2.0 m/s2. Calculate the net force that causes this acceleration. What information are you given? –Mass of water skier = – Acceleration of the water skier = What quantity are you trying to calculate? –The net force –What formula will you use? •Acceleration = Net force ÷ mass •OR Net Force = mass x acceleration •Perform the calculation –Fnet = m x a –F = –F = –F = x kg x m/s2 Practice Problems •What is the net force on a 1,000 kg object accelerating at 3 m/s2? •What net force is needed to accelerate a 25 kg cart at 14 m/s2? Changes in Force and Mass •How can you _______________________________________ of the wagon? •Look again at the equation. •One way to increase acceleration is by ______________________________. •If the _________ is _______________, acceleration and ___________ change in the same way. •So to increase the acceleration of the wagon, you can _________________________________________ used to pull it. •Another way to increase acceleration is to _______________________. •According to the equation, acceleration and _________change in ___________________________________. •If the ____________________________, an increase in ___________ causes a ___________________________________________. •The opposite is also true: A _______________________________ causes an ____________________________________ with a constant ____________. •To increase the acceleration of the wagon, you can _____________________. •So instead of you, the children should _____________________________. •Look at the pictures on the right. •Which vehicle do you think would require a greater force to push? ___________________________ •Why do you think this? ____________________________ ____________________________ ____________________________ •Using the equation, solve for the amount of force. ____________________________ ____________________________