Hey 8th graders! Ready to test your physics prowess? Our free force and motion quiz is designed just for you to explore inertia, gravity, acceleration and velocity in a fun, interactive way. Dive into challenging force and motion questions that stretch your brain, tackle a speedy speed and velocity quiz, conquer the acceleration quiz for grade 8, and uncover how objects move in our inertia and gravity quiz. Whether you're prepping for exam day or just curious, this 8th grade physics quiz will sharpen your skills and build your confidence. Start solving key questions or jump into the ultimate 8th grade physics quiz now - let's ace physics together!
What is inertia?
The tendency of an object to resist changes in motion
A force that accelerates an object
The rate at which velocity changes
The speed of an object in one direction
Inertia is defined as the property of matter that resists changes to its state of motion according to Newton's first law. It means an object will stay at rest or continue moving at constant velocity unless acted upon by a net force. This fundamental concept distinguishes mass from weight and underpins classical mechanics. Learn more.
What is the SI unit for measuring force?
Watt
Newton
Pascal
Joule
A newton (N) is defined as the force required to accelerate a one-kilogram mass by one meter per second squared. It is the standard SI unit for force, named after Sir Isaac Newton. Understanding this unit is vital for solving problems involving forces in physics. Learn more.
According to Newton's first law of motion, an object will remain at rest or in uniform motion unless what occurs?
It loses momentum
Its mass doubles
A net external force acts on it
Its velocity remains constant
Newton's first law states that an object will not change its state of motion unless a net external force acts upon it. This principle is also known as the law of inertia. It explains why seat belts are important when a car stops suddenly. Learn more.
What does acceleration describe?
The rate of change of velocity
The total speed of an object
The amount of inertia an object has
The distance traveled per time
Acceleration measures how quickly an object's velocity changes over time, including both magnitude and direction. It can be positive (speeding up), negative (slowing down), or change in direction. The SI unit is meters per second squared (m/s²). Learn more.
Which quantity describes both speed and direction of motion?
Force
Acceleration
Velocity
Speed
Velocity is a vector quantity that includes both the speed of an object and its direction of motion. In contrast, speed is a scalar and only indicates magnitude. Vectors are key in physics to fully describe motion. Learn more.
What is the approximate acceleration due to gravity on Earth's surface?
32 m/s²
1.6 m/s²
9.8 m/s
9.8 m/s²
The standard acceleration due to gravity at Earth's surface is about 9.8 meters per second squared (m/s²). This value indicates how quickly an object speeds up when falling freely under gravity alone. It is often rounded to 10 m/s² for simplicity in basic calculations. Learn more.
Which term best describes the weight of an object?
The speed gained due to gravity
The amount of matter in the object
The resistance to a change in motion
The gravitational force acting on the object
Weight is the force exerted on an object by gravity and depends on both mass and the local gravitational field strength. It is calculated as W = m · g. Weight is a force, measured in newtons. Learn more.
When forces acting on an object are balanced, what is the net force?
Opposite in direction to motion
Greater than the applied force
Zero
Equal to its mass
Balanced forces are equal in magnitude and opposite in direction, resulting in a net force of zero. When net force is zero, an object maintains its current state of motion. This scenario reflects Newton's first law. Learn more.
What force opposes the motion of objects sliding against each other?
Inertia
Friction
Momentum
Gravity
Friction is the resistive force that occurs when two surfaces move or attempt to move across each other. It always acts opposite to the direction of motion or applied force. Frictional forces are crucial in daily life, from walking to driving. Learn more.
Which of the following is a vector quantity?
Distance
Time
Speed
Displacement
Displacement is a vector quantity because it describes both how far and in what direction an object has moved from its starting point. Distance, speed, and time are scalars since they only describe magnitude. Understanding vectors is essential for analyzing motion. Learn more.
If an object moves at a constant velocity, what is true about the net force acting on it?
It changes direction constantly
It equals mass times velocity
It equals the object's weight
It is zero
A constant velocity means there is no acceleration, which implies the net force acting on the object is zero per Newton's second law. Balanced forces result in no change in motion. If any net force existed, the object would accelerate. Learn more.
A car travels 100 kilometers in 2 hours. What is its average speed?
150 km/h
200 km/h
100 km/h
50 km/h
Average speed is total distance divided by total time. Here, 100 km ? 2 h = 50 km/h. This simple calculation helps describe an object's overall motion. Learn more.
A bicycle slows from 8 m/s to 2 m/s in 3 seconds. What is its acceleration?
-6 m/s²
0.2 m/s²
2 m/s²
-2 m/s²
Acceleration is change in velocity divided by time: (2 m/s - 8 m/s) ÷ 3 s = -6 m/s ÷ 3 s = -2 m/s². The negative sign indicates the bicycle is slowing down. Learn more.
A net force of 20 newtons acts on a 5 kg object. What is the object's acceleration?
4 m/s²
15 m/s²
0.25 m/s²
100 m/s²
Newton's second law states that F = m·a, so acceleration a = F/m = 20 N ÷ 5 kg = 4 m/s². This simple relation connects force, mass, and acceleration. Learn more.
On a velocity - time graph, what does the slope represent?
Force
Acceleration
Momentum
Displacement
The slope of a velocity-time graph is the change in velocity over change in time, which defines acceleration. A steeper slope means greater acceleration. This graphical tool is widely used in kinematics. Learn more.
If an object's mass doubles while the gravitational field strength remains the same, what happens to its weight?
It halves
It stays the same
It doubles
It quadruples
Weight is calculated by W = m·g, so if mass (m) doubles and g is constant, weight also doubles. This direct proportionality is fundamental to understanding weight. Learn more.
What is terminal velocity?
The speed at the equator
The constant speed reached when air resistance equals gravitational force
The maximum speed any object can reach
The initial speed of a falling object
Terminal velocity occurs when the upward drag force from air resistance equals the downward gravitational force, resulting in zero net force and constant speed. No further acceleration occurs at this point. It depends on the object's shape, mass, and cross-sectional area. Learn more.
What is the momentum of a 4 kg mass moving at 3 m/s?
7 kg·m/s
12 kg·m/s
0.75 kg·m/s
4 kg·m/s
Momentum (p) is defined as mass (m) times velocity (v): p = m·v = 4 kg × 3 m/s = 12 kg·m/s. This vector quantity is conserved in isolated systems. Learn more.
Under what condition is momentum conserved in a system?
Friction is present
No external forces act on the system
Mass is variable
Velocity is constant
Momentum conservation holds when the net external force on a system is zero, meaning internal forces cancel out. In such isolated systems, total momentum before and after an interaction remains constant. Learn more.
Identify the correct action - reaction force pair when you push against a wall.
You push on the wall and the wall pushes on you
You push on the wall and gravity pulls you down
Gravity pulls you and the wall pulls the Earth
The wall pushes on the floor and you push on the ground
Newton's third law states that for every action there is an equal and opposite reaction. When you apply force to a wall, the wall applies an equal force back on you. These two forces act on different objects. Learn more.
How far does an object in free fall travel after 3 seconds (ignoring air resistance)?
44.1 m
58.8 m
29.4 m
9.8 m
Using s = ½·g·t², with g = 9.8 m/s² and t = 3 s: s = 0.5 × 9.8 × (3)² = 44.1 m. This formula applies when neglecting air resistance. Learn more.
Two forces of 5 N and 7 N act on an object in the same direction. What is the net force?
-2 N
2 N
35 N
12 N
When forces act in the same direction, you add their magnitudes: 5 N + 7 N = 12 N. This gives the net force on the object. Learn more.
A ball is thrown vertically upward at 20 m/s. Approximately how high will it rise before stopping?
10 m
40 m
20.4 m
80 m
Using energy conservation or kinematic equation v² = u² - 2gh, set final velocity v = 0: h = u²/(2g) = (20²)/(2×9.8) ? 20.4 m. This shows how initial speed relates to maximum height. Learn more.
What is the centripetal acceleration of a car traveling at 8 m/s around a circle of radius 10 m?
10 m/s²
6.4 m/s²
8 m/s²
0.64 m/s²
Centripetal acceleration is given by a = v²/r. Substituting v = 8 m/s and r = 10 m: a = (8²)/10 = 64/10 = 6.4 m/s². It always points toward the center of the circle. Learn more.
On a 30° incline, which component of weight causes the object to slide down the plane?
mg
mg·cos30°
mg·tan30°
mg·sin30°
The component of gravitational force parallel to the incline is mg·sin?. For ? = 30°, this becomes mg·sin30°. The perpendicular component is mg·cos? and does not cause motion down the plane. Learn more.
How does increasing the mass of an object affect its inertia?
It has no effect
It increases inertia
Inertia becomes zero
It decreases inertia
Inertia is directly proportional to mass; an object with more mass resists changes in its motion more strongly. This means heavier objects are harder to start or stop moving. Mass is the quantitative measure of inertia. Learn more.
A rocket propels exhaust gases backward and moves upward. Which principle explains this motion?
Conservation of energy
Newton's first law of motion
Conservation of mass
Newton's third law of motion
Newton's third law states that for every action there is an equal and opposite reaction. The rocket pushes exhaust gases backward (action), and the gases push the rocket forward (reaction). This principle is essential to rocketry. Learn more.
An object of mass 2 kg is acted upon by two horizontal forces: 10 N east and 5 N west. What is its acceleration?
2.5 m/s² east
2.5 m/s² west
7.5 m/s² east
5 m/s² east
Net force = 10 N east - 5 N west = 5 N east. Acceleration a = F/m = 5 N ÷ 2 kg = 2.5 m/s² east. Direction is determined by the larger force. Learn more.
What is the key difference between static friction and kinetic friction?
Static friction is always less than kinetic friction
Static friction acts only uphill
Static friction acts on stationary objects, kinetic friction on moving ones
Kinetic friction prevents motion entirely
Static friction acts when two surfaces are not sliding relative to each other, preventing motion up to a maximum threshold. Kinetic friction acts when surfaces slide past one another and is usually lower than the maximum static friction. This distinction is crucial in many applications. Learn more.
Two perpendicular forces, 3 N north and 4 N east, act on an object. What is the magnitude of the resultant force?
1 N
5 N
12 N
7 N
The resultant of perpendicular vectors is found using the Pythagorean theorem: ?(3² + 4²) = 5 N. The direction can be found using trigonometry if needed. This principle applies to vector addition. Learn more.
If the distance between two masses is doubled, how does the gravitational force between them change?
It stays the same
It becomes half as strong
It doubles
It becomes one-quarter as strong
Newton's law of universal gravitation states that F ? 1/r². Doubling the separation (r) decreases the force to 1/(2²) = 1/4 of its original value. This inverse-square relationship is fundamental in gravitational theory. Learn more.
A 1000 kg car slows from 20 m/s to rest in 10 seconds. What is the magnitude of the force applied (assume straight-line motion)?
2000 N
200 N
20,000 N
500 N
First find acceleration: a = (0 - 20) m/s ÷ 10 s = -2 m/s². Force magnitude F = m·a = 1000 kg × 2 m/s² = 2000 N. The negative sign indicates the force acts opposite the direction of motion. Learn more.
A 0.5 kg ball moving at 10 m/s is brought to rest in 0.02 seconds. What is the average force exerted on the ball?
5 N
250 N
500 N
0.25 N
Impulse equals change in momentum: ?p = m·?v = 0.5 kg × (0 - 10 m/s) = -5 kg·m/s. Average force F = ?p/?t = -5 kg·m/s ÷ 0.02 s = -250 N. The magnitude is 250 N opposite to motion. Learn more.
A stone is thrown vertically upward at 15 m/s. Approximately how long will it take to return to the thrower's hand (ignore air resistance)?
7.65 s
15 s
1.53 s
3.06 s
Total flight time for vertical motion is t = 2·u/g where u = 15 m/s and g = 9.8 m/s². So t ? 2×15/9.8 ? 3.06 s. This accounts for ascent and descent. Learn more.
Why do astronauts experience weightlessness in orbit around Earth?
There is no gravity at their altitude
They are in continuous free fall around Earth
They stop moving relative to Earth
Air resistance cancels gravitational pull
Astronauts in orbit are falling towards Earth but moving forward fast enough to keep missing it, creating a continuous free-fall condition. This makes both astronauts and spacecraft accelerate at the same rate, nullifying normal force and creating weightlessness. Gravity still acts but does not produce the sensation of weight. Learn more.
An airplane flies north at 200 km/h and encounters a crosswind blowing east at 50 km/h. What is the plane's resultant ground speed?
200 km/h
206 km/h
150 km/h
250 km/h
The ground speed is the vector sum of the northward velocity (200 km/h) and eastward wind (50 km/h). The magnitude is ?(200²+50²) ? 206 km/h. Direction can be found using trigonometry. Learn more.
If a cyclist doubles their speed while making a turn of the same radius, how does the required centripetal force change?
It stays the same
It halves
It becomes four times as great
It doubles
Centripetal force is proportional to the square of speed divided by radius: F ? v²/r. Doubling the speed (v ? 2v) yields F ? (2v)² = 4v², quadrupling the force needed. This quadratic relationship is key in circular motion. Learn more.
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Study Outcomes
Identify Net Force -
Determine whether forces are balanced or unbalanced and predict how the net force affects an object's motion in real-world scenarios.
Predict Inertia Effects -
Explain Newton's first law by describing how an object's inertia resists changes in motion until an external force is applied.
Explain Gravitational Interaction -
Understand how gravity acts on objects of different masses and calculate weight based on gravitational force.
Calculate Acceleration -
Use the formula a = Δv/Δt to compute acceleration given changes in velocity and time intervals.
Differentiate Speed and Velocity -
Distinguish between scalar speed and vector velocity and solve problems involving directional movement.
Apply Force and Motion Concepts -
Tackle a variety of force and motion questions to reinforce understanding and prepare for quizzes or exams.
Cheat Sheet
Newton's First Law (Inertia) -
Inertia is an object's resistance to any change in its motion and is directly proportional to its mass. Remember "An object at rest stays at rest…" as a mnemonic for Newton's First Law, originally formulated in 1687 and supported by NASA's physics guides. A heavier object requires more force to overcome its inertia, so mass measures how stubborn it is to movement changes.
Newton's Second Law (Force and Acceleration) -
This law states that net force equals mass times acceleration (F = ma), where F is in newtons, m in kilograms, and a in meters per second squared. For instance, pushing a 2 kg cart with 4 N produces an acceleration of 2 m/s² (4 N = 2 kg × 2 m/s²). Practicing F = ma problems from sources like HyperPhysics helps reinforce how force and acceleration are directly linked.
Newton's Third Law (Action and Reaction) -
For every action force, there's an equal and opposite reaction force, meaning forces always come in pairs. When you jump off a skateboard, your feet push down (action) and the board pushes you upward (reaction), sending you forward. This principle, highlighted in MIT OpenCourseWare, explains everything from walking to rocket propulsion.
Speed vs. Velocity -
Speed is a scalar (distance over time) while velocity is a vector (displacement over time with direction). Use speed = d/t (e.g., 10 m/2 s = 5 m/s) and velocity = Δx/Δt with direction (like 5 m/s north) to solve kinematics questions. A handy mnemonic is "Speed has no direction, Velocity Vects" to keep them straight.
Gravity and Free-Fall Acceleration -
Gravity is the attractive force between two masses, given by F = G·m·m₂/r², and near Earth's surface it causes a constant acceleration g ≈ 9.81 m/s². In free-fall, ignoring air resistance, all objects accelerate downward at g, so a 1 kg rock and a 10 kg rock fall at the same rate. Understanding this concept from university labs and NASA experiments is key to mastering motion under gravity.
