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Newton’s Laws Poster Descriptions
[ These will start at the upper left, and go across and then down, just like reading a book.]
1st Law
Figure skater: To begin moving, a figure skater must apply a force using her skates. Once
in motion, she’ll continue to glide along the ice in a straight line unless she applies
another force.
Hands pulling on rope: When each end of a rope is pulled, the rope will move in the
direction of whoever is pulling harder – whoever is applying more force. In this case, the
magnitude or strength of A (on the right) is greater than that of B (on the left), so the rope
moves to the right.
Snowboarder: Someone riding a snowboard experiences a force due to gravity which
pulls them down. He will move in a straight line unless he applies a force to the board,
changing his direction.
Train: A train is a very massive object, and has a lot of inertia. Once in motion, it is very
difficult to stop, requiring a very large force to slow it.
Table and tablecloth: If a tablecloth is pulled slowly out from under objects on a table,
the objects will slide along with it due to friction (which is a force). If the tablecloth is
snatched out suddenly, the force moving the tablecloth is much larger than the force of
friction, so the objects stay on the table.
Jogger: A jogger experiences many forces while running: gravity, the push of her feet, the
friction of her shoes on the ground, and air resistance. Her legs, together with the friction
of her shoes, overcomes her inertia to propel her forward.
2nd Law
Person throwing a ball: When someone throws a ball, she is applying a force to it and
accelerating it. As soon as she lets go, gravity also applies a force, accelerating the ball
downward.
Cube being pulled to the upper right: A heavy cube sits on a surface. When someone
pulls it to the upper right, there are horizontal and vertical components to the forces, so it
accelerates upward and to the right.
Girl on a swing: When a girl swings, gravity accelerates her downward from the top of
her arc. Her inertia keeps her moving, and the force of the tension in the ropes makes her
move in an arc upwards. Gravity then pulls her down, decelerating her until she stops,
and the motion repeats.
Swivel chair: The velocity of an object is its speed plus its direction. Acceleration is the
change in velocity, so changing the speed and/or the direction of an object is an
acceleration. In a swivel chair, the woman feels a force due to acceleration because her
direction is constantly changing as she spins.
Baseball player: A baseball player applies a large force to a baseball, accelerating it to
high velocity. If the ball had more mass, that same force would not accelerate the ball to
such a high velocity.
Cars: When a driver hits the gas, the wheels apply a force on the ground due to friction.
This force accelerates the car forward. The brakes apply a force to the wheels,
decelerating the car. Can you think of any other accelerators in a car? What about the
steering wheel?
3rd Law
Rocket: A rocket works by propelling mass out the back end at high velocity. The action
of the mass of the burning fuel accelerating out the back end applies an opposite reaction
force to the mass of the rocket, moving it forward. The rocket is not simply pushing
against the ground; this works even in the vacuum of space.
Trucker and ramp: When a man pushes a heavy box up a ramp, he applies a force to the
box, and the box reacts by pushing back. If the man pushes hard enough, he can
overcome gravity and friction, getting the box up the ramp.
Shopper: A woman pushing a shopping cart feels a force backwards applied by the cart
on her.
Box on ramp diagram: Gravity applies a force to a box on a ramp. If there is enough
friction, the ramp will support the weight of the box, applying an equal but opposite force
upwards, so the box doesn’t move. If there is less friction (the ramp is smooth, or oiled),
the force upwards doesn’t balance gravity, and the box accelerates downward.
Baseball player: When a baseball player hits a ball with his bat, the ball reacts by pushing
back on him. The player feels this as a jerk backwards when the bat contacts the ball.
Fish: Fish propel themselves forward by pushing water back, behind them. The water
reacts by pushing the fish in the opposite direction, forward.
Hand pulling rope attached to weight: When a hand pulls a rope attached to a weight, it
applies a force to the weight, and the weight reacts by applying a force in the opposite
direction. The hand feels a tug backwards.
Bridge: Suspension bridges are all about actions and reactions. The main cables push the
support poles down, but the poles react by pushing back with an equal but opposite force.
Cables hanging down from the main cables pull the main cables down, which react by
pulling back on the vertical cables. The roadway hangs from the vertical cables, pulling
them down, and the vertical cables react by holding the roadway up.
Soccer player: When a boy runs up to a ball and kicks it, he applies a force to the ball,
moving it forward. The ball reacts by pushing back against the boy, which he feels as
pressure on his foot when he kicks the ball.
Hammer and nail: A hammer hitting a nail applies a large force to it, and reacts by
pushing back against the hammer. The carpenter feels this as a jolt backwards against his
hand.
4th Law
Girl with yoyo: The yoyo feels a force downward due to gravity. This force is overcome
by the girl applying a force to the string. The yoyo accelerates due to both these forces,
and moves in a circle.
Solar system: All the planets in the solar system orbit the Sun due to its gravity. The inner
planets are closer to the Sun, and feel more gravity, so they move faster.
Astronaut: Gravity goes on forever. An astronaut in orbit is accelerated due to gravity,
but without the balancing force upwards by the ground, she falls freely. Some people call
this “weightlessness”, but that’s not really true. Free fall is a better term.
Newton: Isaac Newton was the person who realized that all massive objects in the
Universe apply the force of gravity to all other massive objects. An apple didn’t really
fall on his head, but he realized that the force acting on a falling apple was the same as
that acting on the Moon—the Earth’s gravity.
Girl falling: A girl jumping on a trampoline feels a moment of free fall because for just a
split second the Earth’s gravity is not balanced by the force of the trampoline upwards.
The gravity due to the girl’s mass applies the same force on the Earth as the Earth’s
gravity on the girl, but because the Earth has so much more mass it does not accelerate
very much at all, while the girl accelerates rapidly.
Bike: Bicyclists are very aware of gravity!