Unit 5: Forces and Motion
Every push, pull, and wobble explained: what makes things speed up, slow down, and stay put, from a coasting bike to a rocket launch.
9 topics · 35 questions
Each topic is a path, not a menu: work down it in order and every question builds on the one above. Click any of them to watch the answer draw itself.
Pushes and Pulls
- How it worksHow does every push or pull count as a force with both a size and a direction?
- Worked exampleFind the combined force on a box if two kids each push it forward with 15 newtons of force at the same time.
- Common mistakeWhy doesn't an object need a constant push to just keep moving in a straight line?
- Going furtherWhat happens to a rolling ball's motion when two equal pushes hit it from opposite sides at once?
- Ties togetherHow does combining pushes and pulls into one net force connect to why tug-of-war comes down to which side pushes harder into the ground?
Your turn1 of 2
Find the combined force on a box if two kids each push it forward with 36 newtons of force at the same time.Speed
- How it worksHow do you calculate speed by dividing the distance something travels by the time it takes?
- Worked exampleFind the speed of a cyclist who travels 30 kilometers in 2 hours.
- Common mistakeWhy doesn't speed alone tell you which direction something is moving?
- Going furtherWhat happens to your calculated speed if you use the total trip time, including stops, instead of just moving time?
Your turn1 of 2
Find the speed of a cyclist who travels 142 kilometers in 7 hours.Balanced and Unbalanced Forces
- How it worksHow do balanced forces cancel out to zero while unbalanced forces cause a change in motion?
- Worked exampleFind whether the forces are balanced: a 50 newton pull to the right and a 30 newton pull to the left on the same box.
- Common mistakeWhy doesn't balanced forces mean no forces at all are acting on an object?
Your turn1 of 2
Find the net force on a box with a 62 newton pull to the right and a 14 newton pull to the left.Friction
- How it worksHow do the tiny bumps on two touching surfaces rub together to create the force of friction?
- Common mistakeWhy doesn't a perfectly smooth-looking surface actually have zero friction?
- Going furtherWhat happens to a sliding box's friction when you add more weight on top of it?
- Ties togetherHow does friction turning motion into heat connect to why rubbing your hands together warms them up?
Your turn1 of 2
Why does a sled glide easily over snow but barely budge on bare pavement?Gravity
- How it worksHow does gravity pull every object with mass toward every other object with mass?
- Common mistakeWhy doesn't a heavier bowling ball fall faster than a lighter tennis ball dropped at the same time?
- Ties togetherHow does gravity pulling all falling objects equally connect to why air resistance is the real reason a feather falls slower than a rock?
Your turn1 of 2
Everything you drop falls down. Why, instead of floating off sideways or upward?Air Resistance
- How it worksHow does air pushing back against a falling object's shape slow it down as air resistance?
- Worked exampleFind which falls faster from the same height, a flat coffee filter or the same filter crumpled into a ball.
- Common mistakeWhy doesn't air resistance mean gravity is pulling any less hard on the paper?
- Going furtherWhat happens to a skydiver's falling speed the instant their parachute opens?
Your turn1 of 2
A flat coffee filter and the same filter crumpled into a tight ball are dropped from the same height. Which one falls faster?Newton's First Law: Inertia
- How it worksHow does an object's inertia make it resist any change to its speed or direction?
- Common mistakeWhy isn't inertia a force pushing you forward, rather than your body simply continuing to move?
- Going furtherWhat happens to a stack of checkers when you flick out the bottom one really fast?
- Ties togetherHow does inertia keeping you moving forward in a braking car connect to why seatbelts exist?
Your turn1 of 2
Why do you lurch forward in your seat when a car slams on its brakes?Newton's Second Law: Force, Mass, and Acceleration
- How it worksHow does the same force produce less acceleration on a heavier object than a lighter one?
- Worked exampleFind the acceleration of a 10 kilogram wagon pushed with a force of 20 newtons.
- Common mistakeWhy doesn't a bigger force always mean a bigger acceleration, if the mass also changes?
- Going furtherWhat happens to a rocket's acceleration as it burns fuel and gets lighter during launch?
Your turn1 of 2
Find the acceleration of a 35 kilogram wagon pushed with a force of 133 newtons.Newton's Third Law: Action and Reaction
- How it worksHow does every action force get matched by an equal and opposite reaction force?
- How it worksWalk me through the action-reaction pair when a swimmer pushes water backward to move forward.
- Common mistakeWhy doesn't the reaction force cancel out the action force if they're equal and opposite?
- Going furtherWhat happens to a balloon the instant you let go of it without tying the end?
Your turn1 of 2
Why does a rowboat drift backward the instant you push off from a dock?