The Power is Yours Trivia Quiz

Answer: Her tendency to maintain a constant state of motion

Inertial mass, which is usually just called mass, is a measure of any object's tendency to keep on moving as it is. If it is at rest, it will stay at rest unless acted on by an unbalanced outside force; if it is moving, it will keep moving in a straight line at a constant speed unless acted on by an unbalanced outside force. This is usually referred to as Newton's First Law, or the Law of Inertia.

Weight is a measure of the force which gravity exerts on an object. In any one place, mass and weight are proportional, but when you go to a place where the force of gravity is stronger or weaker, your weight will increase or decrease without any corresponding change in mass. Size is more precisely called volume, and the tendency of an object to resist spinning is its moment of inertia, a property which depends on both the mass and the shape of the object.

Answer: Try to keep her body as erect as possible, with all flippers close to the body

The moment of inertia, which is what keeps you from spinning rapidly, is determined by the mass of the spinning object, and how that mass is distributed - the farther it is from the central axis of rotation, the harder it is to spin. Holding weights will increase her mass, while crouching into a ball (instead of standing as erect as possible) and extending her limbs will both increase the distance of parts of her body from the centre. If you watch ballet dancers and figure skaters, you can see them control their speed with their arms and/or legs, holding them close to spin faster, and extending them horizontally to slow down.

Answer: Acceleration

Acceleration is a measure of how quickly an object's velocity is changing. Velocity means speed in a specific direction. For Suzie, assuming she is swimming in a straight line as she starts her sprint, the two words can be used interchangeably, and most people use the slightly inaccurate word speed.

However, if she changes direction in the water, even if she keeps swimming at the same speed, she will need to change direction, which means she will once again be accelerating.

Answer: Joules

Work is defined as a change to the energy of a system, and they are both measured in the same units. In the SI system, the joule is equivalent to a kg-m^2/s^2, and is also called a newton-metre, since one joule of energy is produced when one newton of force acts on an object over a distance of one metre.

Other systems use different units for energy: an erg (used if mass is measured in grams, force in dynes and distance in centimetres) is equal to one ten-billionth of a joule; the foot-pound is used if force is measured in pound-force, and distance in feet, and is equal to about 1.3 joules.

Answer: Kinetic energy

Kinetic energy is the energy associated with motion. It is calculated as the object's mass multiplied by the square of its speed (and this time it really is speed, since all that matters is its magnitude, not its direction) divided by two. If Suzie has a typical harp seal mass of 150kg, and she is swimming at a speed of 2 m/s, her kinetic energy would be (150*2*2)/2 = 300J.

Answer: Overcoming the force of friction between herself and the water

The force of friction is an external force which acts on her, reducing her kinetic energy, and she slows down. To prevent this, it is necessary to keep putting energy into the seal-sea system, so she keeps expending energy and exerting her muscles to keep moving.

Answer: 6 newtons

Remembering that the work done is equal to the energy change, 300J must equal the force x 50m. If 300 = 50F, then F must be 6 (and the unit of force in this system of measurement is the newton). It should be noted that this is a simplification of what is going on, as the magnitude of the retarding force will vary with her speed, being more at the start when she is moving more quickly, and less as she comes to rest, but the average gives some insight into what is going on. Since the force is acting to slow her down, physicists would usually show it as -6N, the negative sign showing that it acts in the opposite direction to that in which she is travelling.

Answer: Mass in motion

Momentum is what Newton actually talked about in his second law, which we usually summarize for high school classrooms as Force = mass x acceleration. He actually said that Force = change in momentum / time. For situations in which mass is not changing, the two are equivalent statements, but life gets a lot more complicated if mass is not constant as is the case, for example, when a rocket burns fuel and loses mass. Linear momentum is found by multiplying an object's mass by its velocity (and this time, direction matters). Rotational momentum, relating to spin, is calculated by multiplying the moment of inertia by the angular velocity.

The faster an object is moving, the greater its momentum.

Answer: No

An elastic collision is one in which kinetic energy is conserved. Before the two seals collided, both seals had kinetic energy; afterwards, the two of them were stationary, so they had no kinetic energy. They also had no momentum. Since momentum is always conserved in collisions, this means that Sammy and Suzie must have had the same momentum when they collided. We would need to know Sammy's mass in order to know what speed he was travelling at when they bumped into each other.

Answer: The rate of doing work

Power measures the change of energy (or work done) in a given amount of time. In the SI system, it is measured in watts, where one watt equals one joule per second. Another unit for work is the horsepower, but historically that was a different unit in different places, since it was based on a comparison of the power of steam engines to the power of draft horses, hardly an exact unit. Even now, in different applications the term refers to different amounts of power.

The mechanical (or imperial) horsepower is now defined as exactly 550 foot-pounds per second, approximately 750 watts.