Ch 8 Physics Warmups
Distinguish between linear speed and rotational speed.
Rotational measures the number of rotations.
From Thursdays notes why is the centrifugal force the ladybug feels in the rotating frame called a fictious force?
The feeling the ladybug has is not a force but an inertia which is not a force but a tendency.
A 40kg mass is placed at the 10cm mark. Another mass is placed at the 60cm mark. What is the value for the other mass?
160kg (use f x d=f x d)
Calculate the torque produced by a 50N perpendicular force at the end of a 0.2m long wrench.
10Nm (use f x d)
A 100KG ice skater moves around a bend at 12m/s. The radius of the bend is 6m. What is the amount of friction holding the blade to the ice?
2400N (f=mv² over r)
Calculate the torque produced by the same 50N force when a pipe extends the length of the wrench to 0.5m.
25Nm (f x d)
Calculate the force of friction that keeps a 75kg person sitting on the edge of a horizontal rotating platform when the person sits 2m from the center of the platform and has a tangential speed of 3m/s.
337.5 N (use force=mv² over r)
If a 300N mass is placed at the 0cm mark (50 cm from the fulcrum) at what mark should a 500N mass be placed so that the system would be balanced?
80 cm (if you cannot figure out the prob use f x d=f x d)
If a 120 gram mass is placed at the 25cm mark where should a 500g mass be [placed to balance the system?
56cm (don't forget to convert and use f x d=f x d)
Calculate the tension in a horizontal string that whirls a 2kg toy in a circle of radius 2.5m when it moves at 3m/s on an icy surface.
7.2N (use force=mv² over r)
Is it an inward force or an outward force that is exerted on the clothes during the spin cycle of an automatic washing machine?
Inward force.
Explain why a long pole is more beneficial to a tightrope walker if the pole droops.
It distributes more mass to keep you balanced and lowers the center of gravity
Can an object have more than one center of gravity? Why?
No an object can only have one center of gravity although the center of gravity can change.
Can a force produce a torque when there is no lever arm?
No because there needs to be a lever arm to produce torque.
If you are in a car that rounds a curve, and you are not wearing a seat belt, and you slide across seat and slam against a car door, what kind of force is responsible for your slide-centripetal, centrifugal, or no force? Why is it no force?
No force because of the law of inertia.
If the string that holds a whirling can in its circular path breaks, what kind of force causes it to move in a straight line path-centripetal, centrifugal, or no force? What law of physics supports your answer?
No force occurs by the law of inertia.
How do clockwise and counterclockwise torques compare when a system is balanced?
No rotation occurs.
What does a torque tend to do an object?
Produce rotation.
Distinguish between a rotation and a revolution.
Rotation revolves around an inner axis. Revolution revolves around an outer axis.
What is the relationship between center of gravity and support base for an object in stable equilibrium?
The center of gravity falls in the support base.
In terms of center of gravity, support base, and torque, why can you not stand with heels back to a wall and then bend over to touch your toes and return to stand up position?
The center of gravity moves when you move forward so the center of gravity isn't in line with the support base.
Where is the center of mass of a baseball? Where is its center of gravity? Where are these centers for a baseball bat?
The center of mass is in the geometric center of the baseball. The center of gravity is in the same place. The centers are farther up the baseball bat so weight is distrbuted evenly.
When you whirl a can at the end of a string in a circular path, what is the direction of the force you exert on the can?
The force is exerted toward the can.
Where is the center of mass of a soccer ball?
The geometric center of a soccer ball.
What is meant by the "lever arm" of a torque?
The lever arm is the point of leverage.
When you carry a heavy load such as a bucket of water why do you tend to hold your other arm out horizontally?
The object is so heavy you use your arm to keep yourself upright.
Why is it easier to carry the same amount of water in two buckets, one in each hand, than in a single bucket?
The single bucket throws your center of gravity off balance.
If you toss a stick into the air, it appears to wobble all over the place. Specifically what place.
The stick wobbles around the center of gravity.
Why doesn't the Leaning Tower of Pisa topple over?
The tower's center of gravity lies above its base of support.
Why is the wobbly motion of a single star an indication that the star has one or more planets orbiting around it?
This means it has more weight on one side and causes a difference in center of gravity.
Why must you bend forward when carrying a heavy load on your back?
To distribute your mass so the center of gravity is above your support base.