physics test review outline - 8th grade hard copy
i. newton’s second law of motion (f = m * a)
force, mass, and acceleration relationships
formulas: f = m * a; a = f / m; m = f / a
example: a 0.5 kg ball accelerated at 12 m/s² → find force.
2. comparing objects with different masses
heavier objects need more force for the same acceleration.
if the same force is applied, lighter objects accelerate more.
3. friction and air resistance
net force = applied force - opposing forces (friction or air resistance).
example: soccer ball with gravity 5 n downward, air resistance 3 n upward → find net force and acceleration.
ii. newton’s first law of motion (inertia)
1. objects at rest / in motion stay that way
example: passengers in bumper cars keep moving forward when the cars stop suddenly.
2. inertia and everyday situations
a ball rolling on a flat surface slows due to friction, not because it “runs out of force”.
heavier objects have more inertia (harder to start or stop).
iii. newton’s third law of motion (action-reaction)
1. equal and opposite forces
example: pushing on a diving board → the board pushes back equally in the opposite direction.
rocket launches: gases push down, rocket goes up.

physics test review – 8th grade
newton’s second law of motion (a = f / m)
the formula for force is f = ____ * ____; a = ____ / ____; m = ____ / ____
if mass increases, ____ force is needed to keep the same acceleration.
if the same force is applied, the ____ (lighter/heavier) object will accelerate more.
net force = ____ force - ____ force (like friction or air resistance).
newton’s first law of motion (inertia)
objects at rest will stay at rest, and objects in motion will stay in motion unless ____
in bumper cars, passengers keep moving forward when the car stops suddenly because of ____
____
a ball rolling on the ground eventually stops because of ____
newton’s third law of motion (action-reaction)
for every action, there is an ____ and ____ reaction.
example: a rocket goes up because gases push ____, ____
when you push down on a diving board, the board pushes back in the ____ direction.
balanced vs. unbalanced forces
balanced forces mean there is ____ change in motion.
unbalanced forces cause an object to ____, ____, or change ____
if net force = 0, forces are ____. if net force ≠ 0, forces are ____
motion, speed, and graphs
the formula for speed is speed = ____ ÷ ____
a student runs 100 m in 12.5 seconds. speed = ____ m/s
on a motion graph: steeper slope = ____ speed, flat line = ____ motion

Question

physics test review outline - 8th grade hard copy
i. newton’s second law of motion (f = m * a)
force, mass, and acceleration relationships
formulas: f = m * a; a = f / m; m = f / a
example: a 0.5 kg ball accelerated at 12 m/s² → find force.
2. comparing objects with different masses
heavier objects need more force for the same acceleration.
if the same force is applied, lighter objects accelerate more.
3. friction and air resistance
net force = applied force - opposing forces (friction or air resistance).
example: soccer ball with gravity 5 n downward, air resistance 3 n upward → find net force and acceleration.
ii. newton’s first law of motion (inertia)
1. objects at rest / in motion stay that way
example: passengers in bumper cars keep moving forward when the cars stop suddenly.
2. inertia and everyday situations
a ball rolling on a flat surface slows due to friction, not because it “runs out of force”.
heavier objects have more inertia (harder to start or stop).
iii. newton’s third law of motion (action-reaction)
1. equal and opposite forces
example: pushing on a diving board → the board pushes back equally in the opposite direction.
rocket launches: gases push down, rocket goes up.

physics test review – 8th grade
newton’s second law of motion (a = f / m)
the formula for force is f = ____ * ____; a = ____ / ____; m = ____ / ____
if mass increases, ____ force is needed to keep the same acceleration.
if the same force is applied, the ____ (lighter/heavier) object will accelerate more.
net force = ____ force - ____ force (like friction or air resistance).
newton’s first law of motion (inertia)
objects at rest will stay at rest, and objects in motion will stay in motion unless ____
in bumper cars, passengers keep moving forward when the car stops suddenly because of ____
____
a ball rolling on the ground eventually stops because of ____
newton’s third law of motion (action-reaction)
for every action, there is an ____ and ____ reaction.
example: a rocket goes up because gases push ____, ____
when you push down on a diving board, the board pushes back in the ____ direction.
balanced vs. unbalanced forces
balanced forces mean there is ____ change in motion.
unbalanced forces cause an object to ____, ____, or change ____
if net force = 0, forces are ____. if net force ≠ 0, forces are ____
motion, speed, and graphs
the formula for speed is speed = ____ ÷ ____
a student runs 100 m in 12.5 seconds. speed = ____ m/s
on a motion graph: steeper slope = ____ speed, flat line = ____ motion

Accepted Answer

### 1. Newton’s Second Law of Motion ( $ F = m \times a $ ) - Force, Mass, and Acceleration Relationships
#### Example: A 0.5 kg ball accelerated at $ 12 \, \text{m/s}^2 $ → Find force.
# Explanation:
## Step 1: Identify the formula
We use Newton's second law formula $ F = m \times a $, where $ F $ is force, $ m $ is mass, and $ a $ is acceleration.
## Step 2: Substitute the values
Given $ m = 0.5 \, \text{kg} $ and $ a = 12 \, \text{m/s}^2 $, substitute into the formula:
$ F = 0.5 \times 12 $
## Step 3: Calculate the result
$ 0.5 \times 12 = 6 $
# Answer:
The force is $ 6 \, \text{N} $ (Newtons).

### 2. Comparing Objects with Different Masses
#### a. If the same force is applied, the ______ (lighter/heavier) object will accelerate more.
# Brief Explanations:
From Newton’s second law $ a=\frac{F}{m} $, acceleration $ a $ is inversely proportional to mass $ m $ when force $ F $ is constant. So a lighter object (smaller $ m $) will have a larger $ a $.
# Answer:
lighter

#### b. If mass increases, ______ force is needed to keep the same acceleration.
# Brief Explanations:
Using $ F = m \times a $, if $ a $ is constant and $ m $ increases, $ F $ must increase (direct proportionality between $ F $ and $ m $ when $ a $ is constant).
# Answer:
more

#### c. Net Force = ______ force - ______ force (like friction or air resistance)
# Brief Explanations:
Net force is the applied force minus opposing forces (e.g., friction, air resistance) when forces act in opposite directions.
# Answer:
applied; opposing

### 3. Friction and Air Resistance
#### Example: Soccer ball with gravity $ 5 \, \text{N} $ downward, air resistance $ 3 \, \text{N} $ upward → Find net force and acceleration. (Assume mass of ball $ m = 0.5 \, \text{kg} $)
# Explanation:
## Step 1: Calculate net force
Forces are in opposite directions (gravity downward, air resistance upward). Net force $ F_{\text{net}} = F_{\text{gravity}} - F_{\text{air resistance}} $
$ F_{\text{net}} = 5 - 3 = 2 \, \text{N} $ (downward, since gravity is larger)
## Step 2: Calculate acceleration
Use $ a=\frac{F_{\text{net}}}{m} $, with $ F_{\text{net}} = 2 \, \text{N} $ and $ m = 0.5 \, \text{kg} $
$ a=\frac{2}{0.5}=4 \, \text{m/s}^2 $ (downward)
# Answer:
Net force is $ 2 \, \text{N} $ downward, acceleration is $ 4 \, \text{m/s}^2 $ downward.

### B. Newton’s First Law of Motion (Inertia)
#### 1. Objects at Rest / In Motion Stay That Way
#### Example: Passengers in bumper cars keep moving forward when the car stops suddenly.
# Brief Explanations:
This is due to inertia (Newton’s first law): an object in motion stays in motion unless acted on by an unbalanced force. Passengers’ bodies tend to continue moving forward (their state of motion) when the car stops (external force acts on the car, not immediately on the passengers).
# Answer:
Inertia (passengers’ motion persists due to inertia).

#### 2. Inertia and Everyday Situations
#### a. A ball rolling on a flat surface slows due to friction, not because it “runs out of force”.
# Brief Explanations:
Inertia keeps the ball moving; friction (an unbalanced force) opposes motion and slows it down. No “force of motion” is used up—only external forces (like friction) change motion.
# Answer:
Friction (unbalanced force) slows the ball; inertia keeps it moving until friction acts.

#### b. Heavier objects have more inertia (harder to start or stop).
# Brief Explanations:
Inertia is proportional to mass. Heavier objects (more mass) have greater inertia, so more force is needed to change their motion (start/stop).
# Answer:
Mass (inertia ∝ mass; heavier = more mass = more inertia).

### III. Newton’s Third Law of Motion (Action - Reaction)
#### 1. Equal and Opposite Forces
#### Example: Pushing on a diving board → the board pushes back equally in the opposite direction.
# Brief Explanations:
Newton’s third law: for every action (push on board), there is an equal and opposite reaction (board pushes back). Forces are equal in magnitude, opposite in direction.
# Answer:
Action - reaction (equal magnitude, opposite direction forces).

#### Example: Rocket goes up because gases push ______.
# Brief Explanations:
Rocket gases are pushed downward (action), so the rocket is pushed upward (reaction) with equal force (Newton’s third law).
# Answer:
downward (action force), rocket moves upward (reaction).

#### When you push down on a diving board, the board pushes back in the ______ direction.
# Brief Explanations:
Newton’s third law: reaction force is opposite to action force. If you push down (action), the board pushes up (reaction) in the opposite direction.
# Answer:
opposite (upward, opposite to downward push).

### Motion, Speed, and Graphs
#### 1. The formula for speed is Speed = ______ ÷ ______.
# Brief Explanations:
Speed is defined as distance traveled divided by time taken: $ \text{Speed} = \frac{\text{Distance}}{\text{Time}} $.
# Answer:
Distance; Time

#### 2. A student runs $ 100 \, \text{m} $ in $ 12.5 $ seconds. Speed = ______ m/s.
# Explanation:
## Step 1: Identify the formula
Use $ \text{Speed} = \frac{\text{Distance}}{\text{Time}} $
## Step 2: Substitute values
Distance $ = 100 \, \text{m} $, Time $ = 12.5 \, \text{s} $
$ \text{Speed} = \frac{100}{12.5} $
## Step 3: Calculate
$ \frac{100}{12.5}=8 $
# Answer:
$ 8 \, \text{m/s} $

#### 3. On a motion graph: Steeper slope = ______ speed, flat line = ______ motion.
# Brief Explanations:
In a distance - time graph, slope $=\frac{\text{Distance}}{\text{Time}}=\text{Speed}$. A steeper slope means higher speed (more distance over less time). A flat line means distance is constant (no motion, speed = 0).
# Answer:
higher; no (or constant, but “no motion” is accurate for flat distance - time graph)

### Balanced vs. Unbalanced Forces
#### 1. Balanced forces mean there is ______ change in motion.
# Brief Explanations:
Balanced forces (net force = 0) result in no acceleration (Newton’s first law), so no change in motion (speed or direction remains constant).
# Answer:
no

#### 2. Unbalanced forces cause an object to ______, ______, or change ______.
# Brief Explanations:
Unbalanced forces (net force ≠ 0) cause acceleration (Newton’s second law), which means the object can speed up, slow down, or change direction (all are changes in motion).
# Answer:
speed up; slow down; direction

#### 3. If net force = 0, forces are ______. If net force ≠ 0, forces are ______.
# Brief Explanations:
Net force = 0 → forces are balanced (equal in magnitude, opposite in direction, or multiple forces cancel). Net force ≠ 0 → forces are unbalanced (result in acceleration).
# Answer:
balanced; unbalanced

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QUESTION IMAGE

Question

Explanation:

1. Newton’s Second Law of Motion ( \( F = m \times a \) ) - Force, Mass, and Acceleration Relationships

Example: A 0.5 kg ball accelerated at \( 12 \, \text{m/s}^2 \) → Find force.

Step 1: Identify the formula

Step 2: Substitute the values

Step 3: Calculate the result

Answer:

2. Comparing Objects with Different Masses

a. If the same force is applied, the ______ (lighter/heavier) object will accelerate more.