Learn: 8th grade Science Physics

What is a force?

A) A type of energy stored in objects

B) A push or pull that can change an object's motion

C) The speed of an object over time

D) The mass of an object

B) A push or pull that can change an object's motion.

What is an applied force?

A) A force applied to an object by a person or another object

B) A force that pulls objects toward Earth

C) A force that opposes motion between surfaces

D) The support force a surface exerts

A) A force applied to an object by a person or another object.

What is friction force?

A) A force that pulls objects down

B) A force that opposes motion between surfaces

C) The total force after combination

D) A push from a person

B) A force that opposes motion between surfaces.

What is gravitational force?

A) The attractive force between masses, especially Earth and objects near it

B) The friction between two solid surfaces

C) The force exerted by a stretched spring

D) The force of a hand pushing a box

A) The attractive force between masses, especially Earth and objects near it.

What is normal force?

A) The pull of gravity on an object

B) The support force a surface exerts on an object

C) The friction acting on a rolling ball

D) The net force of a system

B) The support force a surface exerts on an object.

What is net force?

A) The total force after all forces are combined

B) The force of gravity alone

C) The mass multiplied by velocity

D) The friction force

A) The total force after all forces are combined.

What is a balanced force?

A) Forces that are not equal and cause motion

B) Forces that are equal in size and opposite in direction

C) A single force acting on an object

D) Forces acting in the same direction

B) Forces that are equal in size and opposite in direction.

What is an unbalanced force?

A) Forces that are equal and opposite

B) Forces that have a net force of zero

C) Forces that are not equal and cause a change in motion

D) Forces acting only on stationary objects

C) Forces that are not equal and cause a change in motion.

What is a free-body diagram?

A) A graph of speed versus time

B) A drawing that shows all the forces acting on an object

C) An equation for calculating acceleration

D) A map of velocity vectors

B) A drawing that shows all the forces acting on an object.

What does an arrow represent in a free-body diagram?

A) Mass

B) Speed

C) A force

D) Time

C) A force.

What does the direction of an arrow show?

A) The mass of the object

B) The direction the force acts

C) The speed of the object

D) The temperature

B) The direction the force acts.

What does the length of an arrow usually represent?

A) The relative strength of the force

B) The duration of the force

C) The weight of the object

D) The velocity of the object

A) The relative strength of the force.

What is Newton's First Law of Motion?

A) F = ma

B) Objects resist changes in motion unless acted on by an unbalanced force

C) Every action has an equal and opposite reaction

D) Energy cannot be created or destroyed

B) Objects resist changes in motion unless acted on by an unbalanced force.

What is Newton's Second Law of Motion?

A) F = ma

B) Inertia equals mass

C) Action equals reaction

D) Velocity equals distance over time

A) F = ma.

What is Newton's Third Law of Motion?

A) Objects at rest stay at rest

B) F = ma

C) Every action force has an equal and opposite reaction force

D) Acceleration is proportional to mass

C) Every action force has an equal and opposite reaction force.

What is inertia?

A) A change in velocity

B) An object's resistance to a change in motion

C) The force of gravity

D) The speed of an object

B) An object's resistance to a change in motion.

What is an action force?

A) The first force in an action-reaction pair

B) The reaction force

C) The net force

D) Friction

A) The first force in an action-reaction pair.

What is a reaction force?

A) The initial push

B) The equal and opposite force in an action-reaction pair

C) The frictional force

D) The gravitational pull

B) The equal and opposite force in an action-reaction pair.

What is a force pair?

A) Two forces acting on the same object in the same direction

B) Two equal and opposite forces acting on different objects

C) A balanced force and an unbalanced force

D) Gravity and friction

B) Two equal and opposite forces acting on different objects.

What is speed?

A) Distance traveled per unit of time

B) Displacement in a given direction

C) Mass per unit volume

D) Force divided by mass

A) Distance traveled per unit of time.

What is velocity?

A) Speed without direction

B) Speed in a specific direction

C) Acceleration over time

D) Distance times time

B) Speed in a specific direction.

What is acceleration?

A) A change in velocity over time

B) Constant speed in a straight line

C) The total distance traveled

D) Mass times velocity

A) A change in velocity over time.

What is the difference between speed and velocity?

A) Velocity has no direction; speed includes direction

B) Speed has no direction; velocity includes direction

C) They are exactly the same

D) Speed uses different units than velocity

B) Speed has no direction; velocity includes direction.

What is the difference between balanced and unbalanced forces?

A) Balanced forces have a net force of 0 N; unbalanced forces have a nonzero net force

B) Unbalanced forces have a net force of 0 N

C) Balanced forces cause acceleration

D) There is no difference

A) Balanced forces have a net force of 0 N; unbalanced forces have a nonzero net force.

What causes an object to accelerate?

A) Balanced forces

B) An unbalanced net force

C) Constant velocity

D) Zero net force

B) An unbalanced net force.

A book is resting on a table. What force pulls the book downward?

A) Normal force

B) Friction

C) Gravitational force

D) Applied force

C) Gravitational force.

What force pushes upward on the book from the table?

A) Gravitational force

B) Normal force

C) Friction

D) Tension

B) Normal force.

In a free-body diagram of a book resting on a table, should the upward and downward arrows be equal or unequal? Explain.

A) Unequal, because gravity is stronger

B) Equal, because the book is not accelerating vertically

C) Unequal, because of friction

D) Equal, because the book is moving

B) Equal, because the book is not accelerating vertically.

A person pushes a box to the right across the floor. What force points to the right?

A) Friction

B) Gravity

C) Applied force

D) Normal force

C) Applied force.

What force usually points opposite the motion of the box?

A) Gravity

B) Applied force

C) Friction

D) Normal force

C) Friction.

What force points downward on the box?

A) Normal force

B) Gravitational force

C) Friction

D) Applied force

B) Gravitational force.

What force points upward from the floor on the box?

A) Gravity

B) Normal force

C) Friction

D) Tension

B) Normal force.

Draw a free-body diagram for a box being pushed to the right across a rough floor.

A) Arrows: applied force left, friction right, gravity up, normal force down

B) Arrows: applied force right, friction left, gravity down, normal force up

C) Arrows: gravity left, normal force right

D) Arrows: applied force up, friction down

B) Arrows: applied force right, friction left, gravity down, normal force up.

A soccer ball is kicked to the right. What is the applied force?

A) The force from the person's foot on the ball

B) The friction of the grass

C) The weight of the ball

D) The air resistance

A) The force from the person's foot on the ball.

After the soccer ball is kicked, what force may slow it down as it rolls across grass?

A) Gravity

B) Friction

C) Normal force

D) Applied force

B) Friction.

Draw a free-body diagram for a ball rolling to the right while friction acts on it.

A) Arrows: motion/applied force right, friction left, gravity down, normal force up

B) Arrows: friction right, motion left

C) Arrows: gravity up, normal force down

D) Arrows: applied force down

A) Arrows: motion/applied force right, friction left, gravity down, normal force up.

An object has 10 N of force pushing right and 10 N pushing left. What is the net force?

A) 20 N right

B) 10 N left

C) 0 N

D) 20 N left

C) 0 N.

Are the forces in Question 37 balanced or unbalanced?

A) Balanced

B) Unbalanced

C) Accelerating

D) Zero

A) Balanced.

An object has 15 N pushing right and 5 N pushing left. What is the net force?

A) 20 N right

B) 10 N right

C) 10 N left

D) 15 N right

B) 10 N right.

Are the forces in Question 39 balanced or unbalanced?

A) Balanced

B) Unbalanced

C) Equal

D) Zero

B) Unbalanced.

Which direction will the object in Question 39 accelerate?

A) To the left

B) To the right

C) Upward

D) It will not accelerate

B) To the right.

An object has 20 N upward and 20 N downward. What is its net force?

A) 40 N

B) 20 N

C) 0 N

D) 10 N

C) 0 N.

What does a net force of 0 N mean?

A) The forces are balanced and there is no acceleration

B) The object is definitely stationary

C) The forces are unbalanced

D) The object is accelerating

A) The forces are balanced and there is no acceleration.

Does a net force of 0 N always mean the object is not moving? Explain.

A) Yes, 0 N means absolute rest

B) No. It may be moving at a constant speed and direction

C) Yes, motion requires a net force

D) No, it means the object is speeding up

B) No. It may be moving at a constant speed and direction.

A parked car has balanced forces acting on it. Describe the forces.

A) Gravity pulls downward, and the ground pushes upward with equal force

B) Friction pulls it forward

C) The engine pushes it upward

D) Air resistance equals weight

A) Gravity pulls downward, and the ground pushes upward with equal force.

A book falls from a desk. Which force is greater: gravity or air resistance?

A) Air resistance

B) Gravity

C) They are equal

D) Normal force

B) Gravity.

If the downward force on an object is greater than the upward force, what will happen?

A) It accelerates upward

B) It accelerates downward

C) It moves at constant speed

D) It stops moving

B) It accelerates downward.

If the upward force on an object is greater than the downward force, what will happen?

A) It accelerates upward

B) It accelerates downward

C) It remains at rest

D) It falls

A) It accelerates upward.

If the force arrows in a free-body diagram are the same length in opposite directions, what does that show?

A) Unbalanced forces

B) Balanced forces

C) Net force greater than zero

D) Acceleration

B) Balanced forces.

If the right-pointing arrow is longer than the left-pointing arrow, what does that show?

A) Balanced forces

B) An unbalanced force to the right

C) An unbalanced force to the left

D) Zero net force

B) An unbalanced force to the right.

A person pulls a wagon with 30 N to the right while friction pulls with 10 N to the left. Calculate the net force.

A) 40 N right

B) 20 N right

C) 20 N left

D) 30 N right

B) 20 N right.

A sled is pulled left with 40 N while friction acts right with 25 N. Calculate the net force and direction.

A) 65 N left

B) 15 N right

C) 15 N left

D) 40 N left

C) 15 N left.

A toy car has 8 N pushing right and 8 N friction pushing left. Will it accelerate? Explain.

A) Yes, because forces are acting on it

B) No, because the net force is 0 N

C) Yes, to the right

D) No, because it has no mass

B) No, because the net force is 0 N.

A box has 50 N downward gravitational force and 50 N upward normal force. What is the vertical net force?

A) 100 N

B) 50 N

C) 0 N

D) 25 N

C) 0 N.

Describe one situation in which an object experiences applied force, friction, gravity, and normal force at the same time.

A) A book sitting on a shelf

B) A person pushes a box across the floor

C) A ball falling in a vacuum

D) A car parked on a hill

B) A person pushes a box across the floor.

Which Newton's Law explains why a ball stays still until it is kicked?

A) Newton's First Law

B) Newton's Second Law

C) Newton's Third Law

D) Law of Gravitation

A) Newton's First Law.

Which Newton's Law explains why a heavier object needs more force to accelerate the same amount?

A) Newton's First Law

B) Newton's Second Law

C) Newton's Third Law

D) Law of Inertia

B) Newton's Second Law.

Which Newton's Law explains action-reaction force pairs?

A) Newton's First Law

B) Newton's Second Law

C) Newton's Third Law

D) Law of Conservation of Energy

C) Newton's Third Law.

Why does a soccer ball stay at rest before it is kicked?

A) It has too much friction

B) No unbalanced force is acting on it

C) Gravity holds it down

D) Its mass is zero

B) No unbalanced force is acting on it.

Why does a moving skateboard continue moving when no large force stops it?

A) Friction

B) Inertia

C) Gravity

D) Acceleration

B) Inertia.

What is inertia?

A) Resistance to a change in motion

B) The force of a moving object

C) Acceleration due to gravity

D) Speed in a direction

A) Resistance to a change in motion.

Which has more inertia: an empty shopping cart or a full shopping cart? Explain.

A) The empty shopping cart because it moves faster

B) The full shopping cart because of greater mass

C) They have the same inertia

D) The empty shopping cart because of less friction

B) The full shopping cart because of greater mass.

Which has more inertia: a bicycle or a car?

A) A bicycle

B) A car

C) They have equal inertia

D) Neither has inertia

B) A car.

How does mass affect inertia?

A) More mass means less inertia

B) More mass means more inertia

C) Mass has no effect on inertia

D) Inertia is independent of mass

B) More mass means more inertia.

A moving bus stops suddenly. Why do passengers move forward?

A) Their bodies continue moving due to inertia

B) Gravity pulls them forward

C) The seats push them forward

D) Air resistance pushes them

A) Their bodies continue moving due to inertia.

How does wearing a seat belt demonstrate Newton's First Law?

A) It pulls you backward with gravity

B) The seat belt provides a force that stops passengers from continuing forward

C) It increases your mass

D) It eliminates friction

B) The seat belt provides a force that stops passengers from continuing forward.

A ball remains at rest on the ground until someone kicks it. What force changes its motion?

A) Gravity

B) The kicking force

C) Normal force

D) Friction

B) The kicking force.

Does an object need a force to keep moving at a constant velocity? Explain.

A) Yes, motion always requires force

B) No. An object can continue moving at constant velocity without an unbalanced force

C) Yes, to overcome gravity

D) No, only if it is accelerating

B) No. An object can continue moving at constant velocity without an unbalanced force.

What happens to acceleration when the net force increases but mass stays constant?

A) Acceleration decreases

B) Acceleration increases

C) Acceleration stays the same

D) Acceleration drops to zero

B) Acceleration increases.

What happens to acceleration when mass increases but net force stays constant?

A) Acceleration increases

B) Acceleration decreases

C) Acceleration stays the same

D) Acceleration becomes negative

B) Acceleration decreases.

What happens to acceleration when net force decreases but mass stays constant?

A) Acceleration increases

B) Acceleration stays the same

C) Acceleration decreases

D) Acceleration doubles

C) Acceleration decreases.

State Newton's Second Law as an equation.

A) F = m / a

B) F = ma

C) a = m / F

D) m = Fa

B) F = ma.

What do the letters in the equation F = ma represent?

A) F is force, m is mass, and a is acceleration

B) F is friction, m is motion, a is area

C) F is fast, m is momentum, a is action

D) F is force, m is momentum, a is angle

A) F is force, m is mass, and a is acceleration.

Calculate the force needed to accelerate a 5 kg object at 2 m/s².

A) 2.5 N

B) 7 N

C) 10 N

D) 20 N

C) 10 N.

Calculate the acceleration of a 10 kg object acted on by a 30 N net force.

A) 3 m/s²

B) 300 m/s²

C) 20 m/s²

D) 0.33 m/s²

A) 3 m/s².

Calculate the mass of an object acted on by a 20 N force that accelerates at 4 m/s².

A) 80 kg

B) 5 kg

C) 16 kg

D) 24 kg

B) 5 kg.

A 6 kg box is pushed with a net force of 12 N. What is its acceleration?

A) 72 m/s²

B) 6 m/s²

C) 2 m/s²

D) 18 m/s²

C) 2 m/s².

A 3 kg object accelerates at 5 m/s². What net force acts on it?

A) 1.67 N

B) 8 N

C) 15 N

D) 45 N

C) 15 N.

A 40 N net force accelerates an object at 8 m/s². What is its mass?

A) 320 kg

B) 5 kg

C) 48 kg

D) 0.2 kg

B) 5 kg.

Two objects experience the same force. Which object accelerates more: the one with greater mass or less mass?

A) The object with greater mass

B) The object with less mass

C) They accelerate equally

D) Neither accelerates

B) The object with less mass.

Two objects have the same mass. Which one accelerates more: the one with greater force or less force?

A) The one with less force

B) The one with greater force

C) They accelerate equally

D) Neither accelerates

B) The one with greater force.

A 2 kg object has a net force of 18 N. Calculate its acceleration.

A) 36 m/s²

B) 9 m/s²

C) 16 m/s²

D) 20 m/s²

B) 9 m/s².

A 15 kg object accelerates at 2 m/s². Calculate the net force.

A) 7.5 N

B) 13 N

C) 17 N

D) 30 N

D) 30 N.

A 50 N force acts on a 10 kg object. Calculate its acceleration.

A) 500 m/s²

B) 5 m/s²

C) 40 m/s²

D) 0.2 m/s²

B) 5 m/s².

What is an action-reaction force pair?

A) Two forces that are equal and opposite and act on different objects

B) Two forces acting on the same object in the same direction

C) Gravity and normal force

D) Friction and air resistance

A) Two forces that are equal and opposite and act on different objects.

Are action and reaction forces equal in size?

A) No

B) Yes

C) Sometimes

D) Only if stationary

B) Yes.

Are action and reaction forces in the same or opposite directions?

A) Same directions

B) Opposite directions

C) Perpendicular directions

D) Random directions

B) Opposite directions.

Do action-reaction forces act on the same object or different objects?

A) Same object

B) Different objects

C) Always on the ground

D) On no objects

B) Different objects.

A student pushes on a wall. What is the reaction force?

A) The wall falls over

B) The wall pushes back on the student

C) Gravity pulls the student down

D) Friction stops the student

B) The wall pushes back on the student.

A swimmer pushes water backward with their hands. What force moves the swimmer forward?

A) The water pushes the swimmer forward

B) The air pushes the swimmer

C) Gravity pulls the swimmer

D) Friction from the pool floor

A) The water pushes the swimmer forward.

A rocket pushes gases downward. What reaction force moves the rocket?

A) Gravity pulls the rocket down

B) The gases push the rocket upward

C) Air resistance pushes the rocket

D) Friction slows the rocket

B) The gases push the rocket upward.

Identify the action and reaction forces when a person jumps off the ground.

A) Action: person pushes up; reaction: ground pulls down

B) Action: the person pushes down on the ground. Reaction: the ground pushes up on the person

C) Action: gravity pulls down; reaction: normal force pushes up

D) Action: friction pushes forward; reaction: air pushes back

B) Action: the person pushes down on the ground. Reaction: the ground pushes up on the person.

A bird pushes air downward with its wings. What force does the air exert on the bird?

A) The air pulls the bird down

B) The air pushes the bird upward

C) Friction stops the bird

D) No force is exerted

B) The air pushes the bird upward.

Why do action-reaction forces not cancel each other out?

A) They are unequal in size

B) They act in the same direction

C) They act on different objects

D) They occur at different times

C) They act on different objects.

When you walk, what force do your feet apply to the ground?

A) Your feet push backward on the ground, and the ground pushes you forward

B) Your feet push forward on the ground

C) Your feet pull the ground upward

D) Gravity pushes your feet down

A) Your feet push backward on the ground, and the ground pushes you forward.

What is speed?

A) Distance traveled divided by time

B) Displacement multiplied by time

C) Force divided by mass

D) Acceleration over time

A) Distance traveled divided by time.

What is velocity?

A) Speed without direction

B) Speed in a particular direction

C) Distance divided by acceleration

D) Mass times speed

B) Speed in a particular direction.

What is acceleration?

A) The distance an object travels

B) The rate at which velocity changes

C) The speed of an object

D) The force acting on an object

B) The rate at which velocity changes.

A car travels 100 meters in 20 seconds. What is its speed?

A) 2 m/s

B) 5 m/s

C) 2000 m/s

D) 80 m/s

B) 100 ÷ 20 = 5 m/s.

A runner's velocity changes from 2 m/s east to 6 m/s east in 2 seconds. What is the runner's acceleration?

A) 2 m/s² east

B) 4 m/s² east

C) 8 m/s² east

D) 1 m/s² east

A) a = (6 - 2) ÷ 2 = 2 m/s² east.