Newton's 1st Law
The tendency of an object to resist a change in motion.
Inertia
What formula describes Newton's Second Law of Motion?
F = m(a)
Force = mass x acceleration
In science when we talk about fluids, what kinds of substances might be included?
In sciences fluids include both liquids and gases.
What is the speed of an object that travels 80 km in 4 hours? How did you find your answer?
The speed is 20 km/hour. The formula for speed is distance/time, and 80 divided by 4 equals 20.
How many km are in 6,000 m? How did you get your answer?
If you use the ladder method, you need to move your decimal point three spaces to the left, because km is three spaces to the left from m on the ladder. You can also divide 6,000 by 1,000, because there are 1,000 m in a single km. Either way, the answer is that there are 6 km in 6,000 m.
State Newton's First Law of Motion.
An object in motion will remain in motion at a constant velocity unless a force acts on it, and an object a rest will remain at rest unless a force acts on it.
What does it actually mean to say that an object accelerates at a rate of 20 m/s/s?
This means that an object is going faster and faster and faster. Specifically, it is going 20 m/s faster every second that it travels.
If an object is sitting on your desk and is not moving, does it experience a friction force? Explain.
Yes, it is experiencing something called static friction, because friction exists between any two types of matter in contact with each other, even if neither is moving.
Two dogs are fighting over a bone. Dog #1 pulls with a force of 50 N and Dog #2 pulls in the opposite direction with a force of 25 N of force. Which dog won the bone and what was the net force?
The net force was 25 N and Dog #1 won the bone.
What is Newton's Third Law of Motion and how is it related to a rocket launch?
This law states that for every action force there is an equal and opposite reaction force. So when the gases coming from the bottom of the rocket push against the ground, the ground pushes back and the rocket rises up.
Why do we lean to one side when a car goes around a curve?
This is due to inertia. The force is applied to the car for the turn not to our body, and our body wanted to remain in motion at a constant velocity, so it resists the turn.
If two teams are pulling equally in a tug of war game, what is the net force? Why?
The net force in this example is zero Newtons (0 N) because the teams are pulling in opposite directions with equal force, so they offset and balance each other out.
Will a box be easier to slide across a room with carpet or across a hardwood floor? Explain.
In both cases, sliding friction makes it hard to move the box. But the type of surface affects the amount of sliding friction, and the carpet will offer more friction, making the box harder to move, then the hardwood floor, which is smoother and offers less sliding friction.
What is the momentum of an object if the velocity is 10 m/s and the mass of the object is 60 kg? How did you find your answer?
Momentum = mass x velocity, so if you multiply 10 x 60 the answer is 600 kg.m/s
NOTE: The unit of measurement combines the units for velocity and momentum, and the dot in the answer's unit of measurement replaces a multiplication sign.
If there was no friction at all, would that make it easier for everything to move? Use an example to explain.
No, it would not. If there was no static friction, then things would never have any traction to get moving. For example, a car in the snow just ends up spinning its wheels if there is not enough friction between the tires and the snow for it to start. Also, since we don't generally want things to move forever, we need some friction to help stop a moving object.
Compare the role of inertia in projectile and orbital motion.
In projectile motion, once a force is applied, an object in motion will continue to move forward at a constant velocity due to inertia. But it is not moving fast enough to overcome the force of gravity and will eventually fall to the ground in a curved path. In orbital motion, the objects velocity is great enough that gravity cannot overcome inertia, and the object will continue in an almost circular path.
Explain why the clay ball and the friction ball hit the floor at the same or almost the same time every time Mrs. Terrasi dropped them in class, even though the friction ball as 5X the mass of the clay ball.
This is due to the force of gravity, and gravity is a force that exists between any two objects with mass. The strength of the pull depends on the mass of the two objects and the distance between them. Since the Earth is so much more massive than either the clay or the friction ball, it causes both objects to accelerate to the ground at the same rate: 9.8 m/s/s.
Why will it be easier to move a heavy box by putting on something with wheels rather than by dragging it across the floor?
When you put the box on wheels rather than dragging it, the box will experience rolling rather than sliding friction. Since there are only four small points of contact on the wheels touching the ground, there is way less friction than if the entire bottom surface of the box was in contact with the floor, making it much easier to move.
If the force exerted on an object is 100 N and the mass of the object is 5 kg, what is the acceleration? How did you get your answer?
The formula for force is: force = mass x acceleration. So the equation is 100 = 5 x acceleration. You would have to multiply 5 by 20 to get 100, so the acceleration is 20 m/s/s. Notice that another way to get to the answer is to divide 100/5.
If you see a flat, horizontal line on a graph showing distance (y-axis) and time (x-axis), what does that tell you about the speed of the object? What if there is a straight diagonal line from the point of origin? A curved line?
A flat, horizontal line indicates that time is passing but the distance is not changing, so the object is at rest and the speed is 0. A straight diagonal line from the point of origin suggests that the object is moving at a constant speed toward a destination. And a curved line indicates that the object is accelerating, so the speed is changing.
What are some safety features in a car that help keep us safe from inertia in an accident?
If a car comes to a sudden stop, our body wants to continue to move forward at a constant velocity due to inertia. Seatbelts and airbags keep us safe. If a car at rest is struck from behind, the car will move forward but our body wants to remain at rest due to inertia, so it feels like our body is moving back. The seat back and headrest help protect us from injury.
A race car driver is driving at a constant speed on a circular track. Is she accelerating? Explain.
Yes, she is accelerating. Even though her speed is constant (so she is not going any faster or slower), since the track is circular she is constantly changing direction. Acceleration is any change in velocity, and since velocity includes speed AND direction, her velocity is changing, so she is accelerating.
Why does a crumpled piece of paper hit the ground much sooner than a flat piece of paper, if all objects accelerate to the surface of the earth at a rate of 9.8 m/s/s? What might you observe if you did this same experiment on the moon? Why?
Both pieces of paper on Earth experience fluid friction since they are in contact with the air (air resistance). Since the flat piece of paper has a greater surface area, there is more air resistance, which slows it down. On the moon the will both fall slower (there is a slower rate of acceleration due to gravity because the moon has less mass), but they will hit at the same time. There is no atmosphere so no fluid friction.
A car traveling in traffic is moving at only 20 km/h. Then the traffic breaks up and the car accelerates to 80 km/h. It takes about 10 seconds for this to happen. What was the acceleration rate of the car? How did you get your answer?
The formula to find acceleration is :
final velocity - starting(initial) velocity / time
So, 80 km/h - 20 km/h divided by 10 seconds = 6 km/h per second
The acceleration is 6 km/s/s.
How does Newton's Third Law of Motion add to the danger of injury in a car accident?
Inertia (Newton's First Law of Motion) causes us to want to stay in motion or at rest when a force it applied to the car. Safety features protect us, but when we hit the airbag, seatbelt, seat back, or headrest (depending on the force was applied to the car) with a certain amount of force, then that object will react with an equal and opposite force, possibly causing a back an forth motion to our body.