Physical Science Goal 1 Study Guide (Force and Motion)
1. All motion is relative to a selected reference point.
2. Distance and displacement both measure an object’s change in position. Distance is a scalar
quantity and displacement is a vector quantity.
3. Practice: Distance and Displacement: For each of the following, determine the distance and
displacement.
a. Toby walks 3 km north, then turns and walks 4 km east.
i. Displacement= 5 km NE
ii. Distance= 7 km
b. Diamond runs 2 blocks south, then turns and runs 3 blocks east.
i. Displacement= 3.6 blocks SE
ii. Distance 5 blocks
c. Charles runs exactly 2 laps around a 400 meter track.
i. Displacement= 0 m
ii. Distance 800 m
d. Dominic ran 3 blocks north, then 2 blocks west.
i. Displacement= 3.6 blocks NW
ii. Distance= 5 blocks
e. Asia swam 3 complete laps in a 50 meter pool. (1 lap is across and back.)
i. Displacement= 0 m
ii. Distance= 300 m
4. Speed and velocity both measure how fast an object changes in position. Speed is a scalar quantity
and velocity is a vector quantity.
5. Practice: Speed and Velocity (v = d/t)
a. Find the velocity in m/s of a swimmer who swims 110 m toward the shore in 72 s.
1.53 m/s
b. Find the velocity in m/s of a baseball thrown 38 m from third base to first base in 1.7 s.
22.4 m/s
c. Calculate the displacement in meters a cyclist would travel in 5.00 h at an average velocity
of 12.0 km/h to the southwest.
60 km
d. How much time does it take for a student running at an average speed of 5.00 m/s to
cover a distance of 2.00 km?
400 s
6. Acceleration is a relationship between velocity and time. (a = (vf – vi)/t)
7. List three ways that an object can accelerate.
a. Change speed (speed up or slow down)
b. Change direction
c. Change both speed and direction
8. Practice: Acceleration
a. Natalie accelerates her skateboard along a straight path from 0 m/s to 4.0 m/s in 2.5 s.
Find her average acceleration. 1.6 m/s/s
b. A turtle swimming in a straight line toward shore has a speed of 0.50 m/s. After 4.0 s, its
speed is 0.80 m/s. What is the turtle’s average acceleration? 0.075 m/s/s
c. Find the average acceleration of a northbound subway train that slows down from 12 m/s
to 9.6 m/s in 0.8 s. 3.0 m/s/s
d. Marisa’s car accelerates at an average rate of 2.6 m/s2. Calculate how long it takes her car
to speed up from 24.6 m/s to 26.8 m/s. 0.85 s
e. A cyclist travels at a constant velocity of 4.5 m/s westward, and then speeds up with a
steady acceleration of 2.3 m/s2. Calculate the cyclist’s speed after accelerating for 5.0 s.
16 m/s
9. Distance vs. Time graphs
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a. Slope = average speed
b. Draw: Constant speed (in class)
c. Draw: At rest (in class)
d. Draw: Acceleration (in class)
e. The greater the slope of the line, the greater the speed of the object.
Speed vs. Time graphs
a. Slope = average acceleration
b. Draw: constant speed (in class)
c. Draw: at rest (in class)
d. Draw: Acceleration (slowing down) (in class)
e. Draw: Acceleration (speeding up) (in class)
f. The greater the slope of the line, the greater the acceleration of the object.
Momentum: is a relationship between mass and velocity of an object (p = m*v).
An object at rest has zero momentum.
If the velocity of an object is increased, then the momentum will be increased.
If the mass of an object is increased, then the momentum will be increased.
Practice: Momentum
a. Calculate the momentum of the following objects:
i. A 75 kg speed skater moving forward at 16 m/s. 1200 kg*m/s
ii. A 135 kg ostrich running north at 16.2 m/s. 2187 kg*m/s
iii. A 5.0 kg baby on a train moving eastward at 72 m/s. 360 kg*m/s
iv. A seated 48.5 kg passenger on a train that is stopped. 0 kg*m/s
b. Calculate the velocity of a 0.8 kg kitten with a momentum of 5 kg*m/s forward.
6.25 m/s
Weight of an object is a measure of the force of gravity and is the product of its mass and the
acceleration due to gravity: Fg = m*g (g = 9.8 m/s2)
Practice: Fg = m*g (g = 9.8 m/s2)
a. Marian planted pumpkin seed in the spring. The pumpkin she grew weighed 3920 N.
What was its mass? 400 kg
b. What is the weight of a 66 kg astronaut on Earth? (g = 9.8 m/s2) 646.8 N
c. What is the weight of the same 66 kg astronaut on the moon? (g = 1.6 m/s2) 105.6 N
Terminal velocity is the maximum velocity of an object in free fall and occurs when the air resistance
is equal the force of gravity. The greater the mass of the object, the greater the terminal velocity of
the object. The as the speed of an object in free fall increases, the magnitude of air resistance
increases.
Friction: a force that opposes motion of an object.
Classify the frictional force present in a situation such as:
a. Static friction: a book resting on a table
b. Sliding friction: a box pushed across the floor
c. Rolling friction: a ball rolling across the floor
d. Fluid friction: a boat moving through a river
e. Fluid friction: an object in free-fall
The greater the mass of an object, the greater the inertia of an object.
The motion of an object will remain the same (either at rest or moving at a constant speed in a
straight line) in the absence of unbalanced forces. If a change in motion of an object is observed,
there must have been a unbalanced or net force.
The acceleration of an object is directly proportional the force applied and inversely proportional to
the mass of the object.
Practice: F = m*a
a. What is the net force necessary for a 1600 kg automobile to accelerate forward at 2.0
m/s2? 3200 N
b. A baseball accelerates downward at 9.8 m/s2. If the gravitational force is the only force
acting on the baseball and is 1.4 N, what is the baseball’s mass? 0.143 kg
c. A sailboat and its crew have a combined mass of 655 kg. Ignoring frictional forces, if the
sailboat experiences a net force of 895 N pushing it forward, what is the sailboat’s
acceleration? 1.37 m/s/s
d. What is the acceleration of a boy on a skateboard if the unbalanced forward force on the
boy is 15 N? The total mass of the boy and the skateboard is 58 kg. 0.26 m/s/s
e. What force is necessary to accelerate a 1250 kg car at a rate of 40 m/s2? 50,000 N
f. What is the mass of an object if a force of 34 N produces an acceleration of 4 m/s2? 8.5 kg
25. The greater the force on an object, the greater its change in motion; however the same amount of
force applied to an object with less mass results in a greater acceleration.
26. Forces always come in action-reaction pairs due to the interaction between the objects. Whenever
one object exerts a force on another, an equal and opposite force is exerted by the second on the
first. These action-reaction pairs do not “cancel each other out” because they are acting on
different objects.