Define it!
A point against which position is measured.
Reference Point
All motion is relative.
True
(motion depends on the reference point that is used)
To study the motion of an object, this is the first thing you need to know.
Its position
Distance traveled / time traveled = ?
If we take the distance an object travels and divide by the time it takes to travel that distance, we find out this about the object.
its speed (speed is how quickly motion occurs)
10 meters is a: (1) Vector, or (2) Scalar quantity. Identify it as speed, distance, velocity, acceleration, or none of these.
A scalar quantity (it has no direction) – it is only distance (meters)
Velocity = speed + this.
Direction
A physical measurement that contains directional information.
Vector Quantity
If a glass of water sits on a counter, it is not in motion.
False
(it is in motion relative to many reference points – to other objects on earth, including anyone walking towards it)
You are afloat on a still lake and your position relative to shore does not change. Two girls are jogging along the lake in perfect pace with each other. You are in motion relative to ______.
The two girls
In miles per hour, this is the speed of a boat that travels 10 miles in 30 minutes.
20 mph
(Eq. 9.1: speed = distance traveled / time traveled; convert minutes to hours first = 0.5 hours; then 10 miles/0.5 hours = 20 miles/hour)
1.2 meters/second2 east is a: (1) Vector, or (2) Scalar quantity. Identify it as speed, distance, velocity, acceleration, or none of these.
A vector quantity (it has direction) – it is acceleration (distance over time squared)
In physics, you need to know this about any quantities you measure or calculate.
The units involved
(units are just as important as the quantity itself)
A physical measurement that does not contain directional information.
Scalar quantity
If an object’s position does not change relative to a reference point, it is not moving relative to that reference point.
True
(For motion to occur, an object’s position must change.)
You are afloat on a still lake and your position relative to shore does not change. Two girls are jogging along the lake in perfect pace with each other. The 1st girl is in motion relative to ______.
You
When objects travel in the same direction, their relative speed is this calculation of their individual speeds.
The difference (subtraction)
3.4 feet/hour and slowing is a: (1) Vector, or (2) Scalar quantity. Identify it as speed, distance, velocity, acceleration, or none of these.
A scalar quantity (it has no direction) – it is speed (feet/hour)
When objects travel in opposite directions, their relative speed is this calculation of their individual speeds.
The sum (addition)
The time rate of change of an object’s velocity.
Acceleration
(final velocity – initial velocity) / time
St. Thomas Aquinas listed the presence of motion as one of his five arguments for the existence of God.
True
(He said that in all of our experience, humans have found that no motion can occur without a mover. He called God the “original mover.”)
You are afloat on a still lake and your position relative to shore does not change. Two girls are jogging along the lake in perfect pace with each other. The 2nd girl is not in motion relative to ______.
The first girl
In meters per second, this is the speed of a jogger who covers 6 kilometers in 45 minutes.
2.2 meters/second
[Eq. 9.1: speed = distance traveled / time traveled; convert km to m (6,000) and minutes to seconds (2,700); then 6,000 m/2,700 seconds = 2.2 meters/second]
56 liters is a: (1) Vector, or (2) Scalar quantity. Identify it as speed, distance, velocity, acceleration, or none of these.
A scalar quantity (it has no direction) – it is none of these (liters is a volume unit)
In physics, whether the velocity of an object speeds up or slows down, this term is still used to describe it.
Acceleration
(“deceleration” is never used in physics to describe slowing velocity – instead, the direction of acceleration is given)
The motion of an object when it is falling solely under the influence of gravity.
Free fall
A picky physicist says it is impossible for any object to experience free fall near the earth’s surface. This is technically correct.
True
(To be in free fall, an object can only be influenced by gravity. Air resistance is a second influence for all objects.)
This is the physics equation to use for acceleration.
Equation 9.2:
acceleration = (final velocity – initial velocity) / time
This is the physics equation to use for velocity or speed.
Equation 9.1:
speed = distance traveled / time traveled
2.2 miles/minute west is a: (1) Vector, or (2) Scalar quantity. Identify it as speed, distance, velocity, acceleration, or none of these.
A vector quantity (it has direction) – it is velocity (distance over time) (note: it is not also speed because speed is not a vector quantity)
An object might be doing this when its direction changes, even if its speed is not changing.
Accelerating (when an object changes direction but not speed, it is still accelerating)
This force acts upon falling objects in addition to gravity, though we are not considering it in our calculations. It is due to gas molecules and atoms in the air that “resist” the movement of a falling object.
Air resistance
Even though a physicist is correct in saying it is impossible for any object to experience free fall near the earth’s surface, the effect of air resistance is so small on heavy objects that it usually can be ignored.
True
A sports car goes from 0 velocity to 12 meters/second east in 2 seconds. This is the car’s acceleration. (Since speed increases, the acceleration will be in the same direction.)
6 meters/sec2 east
[Eq. 9.2: acceleration = (final velocity – initial velocity) / time; (12 m/s – 0 m/s) / 2 s = 12 m/s / 2 s = 6 m/s2]
A long, vertical glass tube contains a feather and a penny. All the air is pumped out, and the tube is turned upside down, causing both to fall. This object hits the bottom first.
Neither. They both hit at the same time. With no air, there is no air resistance, and they are equally affected by gravity.
2.2 millimeters/year is a: (1) Vector, or (2) Scalar quantity. Identify it as speed, distance, velocity, acceleration, or none of these.
A scalar quantity (it has no direction) – it is speed (mm/year)
A hot air balloonist drops a rock from his balloon. It takes 7 seconds for the rock to hit the ground. This is the balloonist’s altitude in feet. [Remember distance = ½ (acceleration, or 32 feet/second2) x (time)2]
784 feet
[Eq. 9.3: 1/2 x (32 feet/s2) x (7 s)2 = ½ x (32 feet/s2) x (49 s2) = 784 feet]
This branch of physics deals with the study of objects in motion, the forces applied to those objects, and the energy that exists in them.
The science of mechanics
When an object travels for 15 minutes with a constant velocity of 12 mph west, the acceleration is zero (0).
True
(Trick question! Acceleration is the change in velocity. With no change in velocity, there is no acceleration.)
A train traveling 30 mph south takes 12 minutes to slow to a stop when this is its acceleration.
-150 miles/hour2
[Eq. 9.2: acceleration = (final velocity – initial velocity) / time; convert minutes to hours first = 0.2 hours; then (0 miles/h – 30 miles/h) / 0.2 h = -30 miles/h / 0.2 h = -150 miles/hour2]
A scientist studies the acceleration of an object moving in a straight line. He measures the distance the object travels in 30-second time intervals. He finds that in each interval, the object travels a shorter distance than in the previous interval. The direction of the acceleration is (1) the same as, or (2) opposite direction of the velocity.
Opposite direction
A car and truck are traveling north on a highway. The truck’s speed is 45 mph and the car’s is 57 mph. If the truck is ahead of the car, this is the relative velocity.
12 mph towards each other
(relative velocity = 57 mph – 45 mph = 12 mph; the car is catching up to the truck)
This is the height of a building in meters if it takes a dropped rock 4.1 seconds to fall from the roof. [Remember distance = ½ (acceleration, or 9.8 m/s2) x (time)2]
82.4 meters
[Eq. 9.3: 1/2 x (9.8 m/s2) x (4.1 s)2 = ½ x (9.8 m/s2) x (16.81 s2) = 82.4 meters]