Forces
What is the unit of force?
Newtons
What is Newton's first law?
An object at rest remains at rest and an object in motion remains in motion unless acted on by an unbalanced force
What is a collision?
When two objects come in contact with each other
What is the difference between speed and velocity?
Speed measures how far something travels over a given amount of time (distance/time)
Velocity is speed with direction
What is a force?
A push or a pull exerted on an object
What is Newton's 3rd Law
For every action, there is an equal and opposite reaction.
Why is the front of a car design to crumple during a crash?
To increase the time it takes for the collision to occur, decreasing the acceleration of the collision
If a 70-kg swimmer pushes off a pool wall with a force of 250 N, what is her acceleration?
3.57 N
Sasha pulls a block across the floor at a constant speed. Why doesn’t the motion of the block change even though Sasha is pulling on it?
Sasha’s force on the block is balanced by the friction force
What is weight?
The amount of gravitational force on an object
This law explains why your school books will fly forward in a car if you stop suddenly
Newton's 1st Law or Inertia
If two marbles with the same mass were rolled toward each other with the same speed, what would happen when they collide?
They would bounce back in opposite directions at the same speed
Explain how Newton's three laws are applied when two marbles moving toward each other collide.
The two marbles will stay inn motion until acted on by the unbalanced force of the other marble (Newton's First Law)
The acceleration of the marble after the collision depends on the force and mass of the other marble applied during the collision (Newton's Second Law)
When the two marbles collide, there are equal and opposite forces acting on the marbles (Newton's Third Law)
What two things affect gravitational pull?
Mass and Distance
What is the formula for acceleration with Newton's 2nd Law? Define the variables.
acceleration= force/mass or F=ma
F=force
m=mass
a=acceleration
If I pulled a marble from Newton's cradle and let it fall, explain what would happen.
The marble would hit the stationary marbles and transfer the energy to the outer marble. They would move back and forth until enough energy is lost through sound and it stops.
At the start of a hockey game, the referee drops the puck between two players from opposing teams. Each player wants to push the puck in the opposite direction. For several seconds the puck does not move even though both players are pushing on it with their hockey sticks.
Identify the forces acting on the puck AND explain why it does not move.
There are two forces on the puck, one force from the first hockey stick, and the other force in the opposite direction from the other hockey stick.
The two forces acting on the puck are balanced at first, because both players are pushing in opposite directions with equal force.
What is the difference between contact and non-contact forces? Provide two examples for each.
Contact forces occur when two object are touching. Non-contact forces are present when the two objects are not touching.
Examples:
Contact: Friction, air resistance
Non-contact: Gravitational, magnetic, electrostatic
Chini is sliding blocks of different materials down a steel ramp. All of the blocks have similar sizes and masses. The list below shows the coefficient of friction for several materials when sliding on steel. The larger the coefficient of friction, the greater the force of friction. Which block would reach the bottom the fastest and which is the slowest?
Aluminum: .25
Chromium: .21
Glass: .12
Steel: .23
Titanium alloy: .31
Glass slides down the fastest
Titanium slides down the slowest
How much force is needed to push a 10 g box at 2 m/s/s?
20 N
Person A has a mass of 100 kg and Person B has a mass of 50 kg. They are both moving at the same speed toward one another. What will happen when they collide?
Person A and Person B will be moving opposite their original direction of travel. Person B will be moving backwards more quickly than Person A
Christian is riding his bicycle. He finds that he can accelerate from rest at 0.44 m/s2 for 5 s to reach a speed of 2.2 m/s. The total mass of Christian and his bicycle is 54 kg. Later, he straps some cargo onto the back of his bicycle. The mass of the cargo is 12 kg.
Calculate the force that Christian can exert on his bicycle before picking up the cargo and exerts the same force on his bicycle.
AND
Calculate the acceleration of the bicycle when Christian adds the cargo and exerts the same force on his bicycle.
Force he can exert: 23.8N
Acceleration: .36 m/s/s