Module 5 Review questions Flashcards
What are Newton’s three laws?
- An object in motion (or at rest) will tend to stay in motion (or at rest) until it is acted on by an outside force.
- When an object is acted on by one or more outside forces, the vector sum of those forces is equal to the mass of the object times the resulting acceleration vector.
- For every action there is an equal and opposite reaction.
Why will friction always be present when two surfaces touch each other?
Matter is composed of atoms, and the atoms of the one surface will attract the atoms of the other surface.
A man is riding a horse at a quick gallop. Suddenly, the horse stops dead in its tracks. When this happens, the rider flies out of the saddle and lands on the ground. Does the rider fly forward over the horses head, or backwards over the horses rump? Use Newton’s first law to explain your answer.
The man will fly forward, over the horse’s head. The Law of Inertia tells us that on object in motion (the man) stays in motion until acted on by an outside force. The man is moving with the velocity of the horse. When the horse stops, the man is still moving. The force of friction between the man and the his saddle is not enough to stop the motion, the man cannot stop moving forward.
A student applies the same force to two objects. If the first is 1,000 times more massive that the second, which accelerates more quickly? How much more quickly?
The less massive object will accelerate 1,000 times faster than the more massive object.
Which of the following are legitimate force units?
pound, slug, kg x m/sec, slug x mile / hr^2
slug x mile / hr^2 and pound
A physics student measures an object and writes down a value of 13.1 Newtons. What was the student measuring the object’s mass or its weight?
The student was measuring weight.
A physicist uses the same scale to measure the mass of an object at two different locations: Death Valley and the top of Mount Everest. Is the measurement accurate in both locations? Why or why not?
The mass will not be accurate at one of the locations. The scale must measure weight, and it converts to mass by dividing by the acceleration due to gravity. The acceleration due to gravity depends on position, however. Thus, if the number that the scale divides by is right for one of the locations, it will not be right for the other.
What is normal force? Why is it important in physics?
The normal force is the force exerted by a surface supporting an object. It is primarily used to determine frictional force.
A physics student is measuring frictional coefficients. For one surface, he measures the coefficients but neglects to write down which is the static coefficient, and which is the kinetic one. If the numbers are 0.23 and 0.54, which is which?
The static coefficient of friction is always greater. 0.54 is static and 0.23 is kinetic.
When a tire rolls on a road, it pushes against the road. According to Newton’s third law, what must happen in response to this push?
The road must respond by pushing the tire.
