02 Forces and Motion

Explain: Force

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

Explain: Motion

A change in an object's position compared with a reference point.

Explain: Reference point

An object or place used to decide whether another object's position has changed.

Explain: Push

A force directed away from the person or object applying it.

Explain: Pull

A force directed toward the person or object applying it.

Explain: Spring scale

A tool used to measure the strength of a force.

Explain: Newton

The metric unit of force, written with the symbol N.

Explain: Spring-scale indicator

The part of a spring scale that points to the measured force on its marked scale.

Explain: Force starting motion

A change such as a resting soccer ball beginning to move after a kick.

Explain: Force stopping motion

A change such as a moving bicycle coming to rest when brakes are applied.

Explain: Force changing speed

A push or pull making a moving object speed up or slow down.

Explain: Force changing direction

A push or pull turning a moving object onto a different path.

Explain: Force and energy transfer

A push or pull passing energy to an object and potentially changing its motion.

Explain: Effect of a stronger push

For the same object and conditions, a greater applied force produces a greater change in motion.

Explain: Effect of greater mass

For the same change in motion, a more massive object needs a greater force.

Explain: Heavier backpack comparison

Moving a 7 kg backpack in the same way as a 4 kg backpack generally requires more force.

Explain: Balanced forces

Forces that cancel one another, giving zero net force and no change in motion.

Explain: Opposite equal forces

A pair of same-strength forces acting in opposite directions, such as 5 N left and 5 N right.

Explain: Rest under balanced forces

A motionless object remaining motionless because the forces on it cancel.

Explain: Moving under balanced forces

An object continuing at the same speed and direction when its net force is zero.

Explain: Unbalanced forces

Forces that do not cancel and therefore cause a change in motion.

Explain: Net force

The combined effect of all forces acting on an object, including their directions.

Explain: Opposite-force subtraction

Finding net force by subtracting opposite forces; 8 N right and 3 N left give 5 N right.

Explain: Same-direction force addition

Combining forces that act the same way; 4 N right and 3 N right give 7 N right.

Explain: Unequal tug-of-war pulls

A situation in which the rope's motion changes toward the side with the greater net pull.

Explain: Support force on a resting book

The table's upward push that balances Earth's downward gravitational pull on the book.

Explain: Testable investigation question

A question that can be answered with observations or measurements from a planned test.

Explain: Variable

A factor that can change and affect an investigation.

Explain: Independent variable

The factor deliberately changed by the investigator.

Explain: Dependent variable

The result measured or observed in response to the changed factor.

Explain: Controlled variable

A factor kept the same so a comparison is fair.

Explain: Fair test

An investigation changing one independent variable while keeping other relevant factors the same.

Explain: Ramp-height independent variable

The height of the ramp when testing how ramp height affects a toy car's travel distance.

Explain: Ramp-height dependent variable

The distance the toy car travels when ramp height is the factor being changed.

Explain: Ramp-test controls

Keeping the same car, surface, and release method while changing ramp height.

Explain: Meter stick in a motion test

A measuring tool used to record how far a toy car travels.

Explain: Data table

An organized arrangement of measurements that makes trial results easier to compare.

Explain: Friction

A contact force between surfaces that opposes sliding or attempted sliding.

Explain: Walking traction

Helpful friction between shoes and the ground that reduces slipping.

Explain: Bicycle braking friction

Rubbing forces in the brakes that slow the wheels and the bicycle.

Explain: Rough-surface friction

The tendency for rougher surfaces to resist sliding more strongly in typical classroom comparisons.

Explain: Lubrication

Adding oil or a similar material between surfaces to reduce friction and wear.

Explain: Wheels reducing resistance

Using rolling rather than dragging to make a heavy object easier to move.

Explain: Harmful friction

Rubbing that wears down machine parts or produces unwanted heat.

Explain: Gravity

The attractive force between objects with mass.

Explain: Direction of Earth's gravity

Toward the center of Earth, which is why a tossed ball falls back down.

Explain: Sun's gravitational role

The Sun's pull that keeps planets following orbits around it.

Explain: Magnetic poles

The ends of a magnet, where its magnetic effects are strongest.

Explain: Opposite magnetic poles

A north pole and a south pole, which attract each other.

Explain: Like magnetic poles

Two north poles or two south poles, which repel each other.

Identify the concept or example: A push or pull that can change an object's motion.

Force

Identify the concept or example: A change in an object's position compared with a reference point.

Motion

Identify the concept or example: An object or place used to decide whether another object's position has changed.

Reference point

Identify the concept or example: A force directed away from the person or object applying it.

Push

Identify the concept or example: A force directed toward the person or object applying it.

Pull

Identify the concept or example: A tool used to measure the strength of a force.

Spring scale

Identify the concept or example: The metric unit of force, written with the symbol N.

Newton

Identify the concept or example: The part of a spring scale that points to the measured force on its marked scale.

Spring-scale indicator

Identify the concept or example: A change such as a resting soccer ball beginning to move after a kick.

Force starting motion

Identify the concept or example: A change such as a moving bicycle coming to rest when brakes are applied.

Force stopping motion

Identify the concept or example: A push or pull making a moving object speed up or slow down.

Force changing speed

Identify the concept or example: A push or pull turning a moving object onto a different path.

Force changing direction

Identify the concept or example: A push or pull passing energy to an object and potentially changing its motion.

Force and energy transfer

Identify the concept or example: For the same object and conditions, a greater applied force produces a greater change in motion.

Effect of a stronger push

Identify the concept or example: For the same change in motion, a more massive object needs a greater force.

Effect of greater mass

Identify the concept or example: Moving a 7 kg backpack in the same way as a 4 kg backpack generally requires more force.

Heavier backpack comparison

Identify the concept or example: Forces that cancel one another, giving zero net force and no change in motion.

Balanced forces

Identify the concept or example: A pair of same-strength forces acting in opposite directions, such as 5 N left and 5 N right.

Opposite equal forces

Identify the concept or example: A motionless object remaining motionless because the forces on it cancel.

Rest under balanced forces

Identify the concept or example: An object continuing at the same speed and direction when its net force is zero.

Moving under balanced forces

Identify the concept or example: Forces that do not cancel and therefore cause a change in motion.

Unbalanced forces

Identify the concept or example: The combined effect of all forces acting on an object, including their directions.

Net force

Identify the concept or example: Finding net force by subtracting opposite forces; 8 N right and 3 N left give 5 N right.

Opposite-force subtraction

Identify the concept or example: Combining forces that act the same way; 4 N right and 3 N right give 7 N right.

Same-direction force addition

Identify the concept or example: A situation in which the rope's motion changes toward the side with the greater net pull.

Unequal tug-of-war pulls

Identify the concept or example: The table's upward push that balances Earth's downward gravitational pull on the book.

Support force on a resting book

Identify the concept or example: A question that can be answered with observations or measurements from a planned test.

Testable investigation question

Identify the concept or example: A factor that can change and affect an investigation.

Variable

Identify the concept or example: The factor deliberately changed by the investigator.

Independent variable

Identify the concept or example: The result measured or observed in response to the changed factor.

Dependent variable

Identify the concept or example: A factor kept the same so a comparison is fair.

Controlled variable

Identify the concept or example: An investigation changing one independent variable while keeping other relevant factors the same.

Fair test

Identify the concept or example: The height of the ramp when testing how ramp height affects a toy car's travel distance.

Ramp-height independent variable

Identify the concept or example: The distance the toy car travels when ramp height is the factor being changed.

Ramp-height dependent variable

Identify the concept or example: Keeping the same car, surface, and release method while changing ramp height.

Ramp-test controls

Identify the concept or example: A measuring tool used to record how far a toy car travels.

Meter stick in a motion test

Identify the concept or example: An organized arrangement of measurements that makes trial results easier to compare.

Data table

Identify the concept or example: A contact force between surfaces that opposes sliding or attempted sliding.

Friction

Identify the concept or example: Helpful friction between shoes and the ground that reduces slipping.

Walking traction

Identify the concept or example: Rubbing forces in the brakes that slow the wheels and the bicycle.

Bicycle braking friction

Identify the concept or example: The tendency for rougher surfaces to resist sliding more strongly in typical classroom comparisons.

Rough-surface friction

Identify the concept or example: Adding oil or a similar material between surfaces to reduce friction and wear.

Lubrication

Identify the concept or example: Using rolling rather than dragging to make a heavy object easier to move.

Wheels reducing resistance

Identify the concept or example: Rubbing that wears down machine parts or produces unwanted heat.

Harmful friction

Identify the concept or example: The attractive force between objects with mass.

Gravity

Identify the concept or example: Toward the center of Earth, which is why a tossed ball falls back down.

Direction of Earth's gravity

Identify the concept or example: The Sun's pull that keeps planets following orbits around it.

Sun's gravitational role

Identify the concept or example: The ends of a magnet, where its magnetic effects are strongest.

Magnetic poles

Identify the concept or example: A north pole and a south pole, which attract each other.

Opposite magnetic poles

Identify the concept or example: Two north poles or two south poles, which repel each other.

Like magnetic poles