Meet the Forces
A push or a pull that changes how an object moves.
What happens to an objects motion when the forces acting on it are balanced?
Its speed and direction stay exactly the same (it either stays completely still or keeps moving at a constant speed).
What is friction?
A contact force that slows down moving objects by rubbing against them in the opposite direction of their motion.
What is gravity?
An invisible, non-contact force that pulls all objects down toward the center of the Earth.
What is inertia?
An object's natural tendency to resist any change to its current state of motion (lazy objects want to stay still, moving objects want to keep moving).
What is a contact force?
A type of force where two objects must physically touch, like kicking a soccer ball or pushing a swing.
What is an unbalanced force?
A force that is not canceled out by another force, which is required to make an object start moving, stop, or change direction.
Why does a skateboard slow down much faster on a grass field than on a smooth concrete sidewalk?
Because rough surfaces like grass create much more friction than smooth surfaces.
What is mass?
The measurement of exactly how much matter or "stuff" is inside an object (this stays the same anywhere in the universe).
How does an object's mass affect its inertia?
The more mass an object has (like a giant school bus), the more inertia it has, making it much harder to speed up, slow down, or turn.
What is a Newton?
The unit of measurement used by scientists to show how strong a force is (abbreviated with a capital "N").
What is net force?
The total combination of all the different forces pushing or pulling on a single object.
What is air resistance?
A type of friction that happens when air particles push upward against a falling object, like a wide parachute catching the air.
What is weight?
The measurement of the pull of gravity on an object's mass (this changes depending on what planet you are standing on).
Why does your body fly forward against your seatbelt when a car suddenly slams on its brakes?
Because of inertia your body was moving forward at the speed of the car, and it wants to keep moving forward even when the car stops.
What is a non-contact force?
A type of force that can pull or push an object from a distance without touching it, like gravity or magnetism.
If two equal teams pull a tug-of-war rope in opposite directions with 50 Newtons of force each, what is the net force?
Zero Newtons (the rope will not move because the forces are balanced).
What would happen to a hockey puck hit in deep space where there is no air or friction?
It would keep sliding forward in a straight line at the exact same speed forever.
Why do astronauts weigh much less on the Moon than on Earth?
The Moon is smaller and has less mass than Earth, meaning its gravitational pull is much weaker.
If you push a tennis ball and a heavy bowling ball with the exact same amount of force, which one speeds up faster?
The tennis ball speeds up faster because it has less mass resisting your push.
What are balanced forces?
Forces that are equal in size but opposite in direction, meaning they perfectly cancel each other out and cause no change in motion.
A toy car is pushed to the right with 10 N of force, while friction pulls it left with 3 N. What is the net force and direction?
7 Newtons to the right (10N - 3N = 7N).
What is one everyday example of friction being helpful to humans?
The friction between your shoes and the floor stopping you from slipping, or car brakes slowing down a vehicle.
If you drop a heavy bowling ball and a light feather at the same time inside a special vacuum chamber with no air, which hits the ground first?
They will hit the ground at the exact same time (gravity pulls all masses down at the same speed when air resistance is removed).
According to Newton's laws of motion, what must you increase if you want a heavy object to speed up just as fast as a light object?
You must increase the amount of force (give it a much bigger push).