Questions and Answers
When you push horizontally on a crate on a level floor that doesn't slide, how great is the force of friction on the crate?
The amount of force applied is equal to the amount of friction force opposing it.
Once the crate is sliding, how hard do you push to keep it moving at constant velocity?
You must push with the same force that is equal to the opposing friction force.
The force of friction for a sliding object varies with speed.
False
Which is more fundamental: mass or weight? Which varies with location?
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What is the Standard International unit for mass?
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What is the Standard International unit for force?
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What is the weight of a 1-kilogram brick resting on a table?
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In the string-pull illustration, does a sharp jerk on the bottom string result in the string breaking because of the ball's weight or its mass?
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State Newton's second law of motion.
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If the net force acting on a sliding block is somehow tripled, what happens to the acceleration?
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If the mass of a sliding block is tripled at the same time the net force on it is also tripled, how does the resulting acceleration compare with the original acceleration?
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What is the condition for an object experiencing free fall?
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Why doesn't a heavy object accelerate more than a light object when both are freely falling?
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What is the net force that acts on a 10-N falling object when it encounters 4 N of air resistance?
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What is the acceleration of a falling object that has reached its terminal velocity?
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How long does the force you exert on a ball last after you toss it upward?
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If a motorcycle moves with a constant velocity, can you conclude that there is no net force acting on it?
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If a motorcycle is moving with constant acceleration, there is no net force acting on it.
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Why don't differences in gravitational forces affect the accelerations of falling objects?
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Study Notes
Force of Friction
- The force of friction on a non-sliding crate equals the applied force.
- Once sliding, to maintain constant velocity, push with a force equal to the opposing friction force.
Friction and Speed
- The force of friction for a sliding object remains constant regardless of its speed.
Mass vs. Weight
- Mass is fundamental; it does not change with location, whereas weight varies with location.
Units of Measurement
- Standard International unit for mass: kilogram (kg).
- Standard International unit for force: newton (N), not pounds (lb).
Weight of Objects
- A 1-kilogram brick exerts a weight of about 9.8 newtons on a table.
Newton's Second Law
- Acceleration is directly proportional to net force acting on an object and inversely proportional to its mass: Acceleration ~ Net Force / Mass.
Impact of Net Force and Mass on Acceleration
- Tripling the net force on a sliding block results in tripled acceleration.
- If both net force and mass are tripled, the acceleration remains unchanged due to equal changes in force and mass.
Free Fall Conditions
- An object is in free fall when gravity is the only force acting on it, with no other forces like friction.
Acceleration in Free Fall
- In free fall, all objects, regardless of weight, accelerate at the same rate due to gravity.
Net Force in Free Fall Conditions
- A 10-N falling object encountering 4 N of air resistance experiences a net force of 6 N. If encountering 10 N of air resistance, the net force is zero.
Terminal Velocity
- At terminal velocity, the acceleration of a falling object is zero, leading to constant velocity.
Force Duration on an Object
- The force exerted on a ball lasts until it reaches its apex height, where gravity and applied force equalize, resulting in a net force of zero.
Constant Velocity and Acceleration
- A motorcycle moving with constant velocity has no net force acting on it. Constant acceleration indicates a net force is present.
Gravitational Forces and Acceleration
- Differences in gravitational forces do not affect accelerations in free fall because the effects of mass and gravitational force balance each other out.
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Test your understanding of Newton's Second Law of Motion with these flashcards. Each card focuses on concepts such as friction and forces acting on objects in motion. Perfect for physics students looking to reinforce their knowledge.
