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A force that opposes motion resulting from the contact of two surfaces
The tendency of an object to resist changes in its velocity
Define kinetic friction
Friction that opposes motion once the motion has already started
State Newton's 1st Law of motion
An object in motion (or at rest) will tend to stay in motion (or at rest) until it is acted upon by an outside force.
State Newton's 2nd Law of motion
When an object is acted on by one or more outside forces the total force is equal to the mass of the object time the resulting acceleration.
State Newton's 3rd Law of motion
For every action there is an equal and opposite reaction
Define static friction
Friction that opposes the initiation of motion
In space there is almost no air so there is virtually no friction. If an astronaut throws a ball in space with an initial velocity of 3.0 meters per second to the west what will the balls velocity be in a year? Assume there are no nearby planets.
3.0 meters per second
A boy is running north with a bean bag in his hands. he passes by a tree as soon as he is besides the tree, he drops the beanbag. Will it land by the tree or will it land south of the tree or north?
the boy is running but now his friend stands beside the tree with the beanbag. as the boy passes he barely taps the beanbag causing it to fall out his friends hands. will it land next to the tree ? or will it be north or south of the tree?
next to the tree
a busy shopper is driving down the road. many boxes lie piled in the back seat of the car evidence of shopping activity. suddenly the shopper must hit the brake to avoid a collistion . will the boxes be slammed further back into the seat ofr will they fly forward where the driver can feel them.
When roads get wet they can get slick. Obviously then friction between a car's tires and the road decreases when the road is wet. Why?
the water fills in the cracks in the road making the road smoother therefore reducing the friction
In order to slide a refrigerator across the floor, a man must exert an enormous amount of force. Once it is moving however, the man need not exert nearly as much force to keep it moving. Why?
The static frictional force is greater than the kinetic frictional force
A child is pushing her toy across the room with a constant velocity to the east. If the static friction between the toy and the floor is 15 Newtons, while the kinetic friction is 10 Newtons, what force is the child exerting?
10 Newtons to the west
A father is trying to teach his child to ice skate. As the child stands still, the father pushes him forward with an acceleration of 2.0 meters per second2 north. If the child's mass is 20 kg, what is the force with which the father is pushing?
In order to get a 15 kg object moving to the west a force of more than 25 Newtons must be exerted. Once it is moving however, a force of only 20 Newtons accelerates the object at 0.1 meters per second2 to the west. What is the force that static friction can exert on an object? What is the force of kinetic friction?
static force: 25 newtons to the east
kinetic force: 18.5 newtons to the east
Static friction can exert a force of up to 700 newtons on a 500 kg box of bricks. The kinetic frictional force is only 220 Newtons. How many Newtons of force must a worker exert to get the box moving? What force must the worker exert to accelerate the box at 0.1 meters per second2
to the south?
total force= 50 netons
f? - 220 = 50 = 220+ 50= 270 newtons to the south
In order to shove a rock out the way a gardener gets it moving by exerting just slightly more than 100 newtons of force . to keep it moving at a constant velocity eastward , however the gardener only needs to exert 45 newton force to the east . what are the static and kinetic frictional forces between the rock and the ground?
Two men are trying to push a 710 kg rock . The first exerts a force of 156 Newtons east and the second exerts a force of 220 Newtons east. The rock accelerates at 0.20 meters per second2 to the east. What is the kinetic frictional force between the rock and the ground?
A child pushes against a large doghouse trying to move it. The dog house remains stubbornly unmoved. What exerts the equal and opposite force which Newton's 3rd law of motion says must happen in response to the child's push? what is that force exerted on?
the equal and opposite force is exerted by the doghouse on the child
In a baseball game a player catches a fast moving ball. The ball stops in the player's hand. What evidence tells you that the player exerted a force on the ball? What exerts the equal and opposite force required by Newton's 3rd law? What evidence does the player have for this force?
the balls velocity changed ( it stopped moving)
the player exerts the equal opposite force and evidence by the pain felt from the ball
A man leans up against a wall with a force of 20 newtons to the east . What is the force exerted by the wall on the man?
20 Newtons to the west
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