Modules 2/3 Review: Motion, Forces, Newton's Laws

force

a push or pull upon an object

balanced force

when forces on an object are of equal magnitude and in opposite directions; no acceleration; 0 net force

unbalanced force

when forces on an object do not cancel out; causes acceleration; net force is not 0

net force

the sum of all the forces acting on an object; add forces in same direction, subtract forces in opposite directions.

friction

a force that opposes motion between two surfaces that are in contact

inertia

the tendency of an object to resist a change in motion unless an outside force acts on it

weight

the measure of the force of gravity on an object; F=mg

gravitational strength

the attractive force existing between any two objects that have mass; the greater the objects' mass the greater the gravitational strength; the shorter the distance the greater the gravitational strength

Mass

The amount of matter in an object

Newton

the SI unit for force, (1N=1kg∙m/s²)

Acceleration

The change in velocity over time

You are riding a bike, you hit a rock and you fly off the bike into the mud in front of the bike.

Example of Newton's 1st Law; inertia

Newton's Second Law of Motion

The acceleration of an object depends on the mass of the object and the amount of force applied. The greater the force, the greater the acceleration. The greater the mass, the lesser the acceleration.

A little kid and his dad are skipping pebbles on the pond. The pebbles that the dad throws accelerate faster than the little kid's pebbles.

Example of Newton's 2nd Law

Normal Force (Fn)

a force that acts on a surface in a direction perpendicular to the surface

Tension (Ft)

the pull exerted by a string, rope, or cable when attached to a body and pulled taut

Force Diagram (also called a Free Body Diagram)

a simple drawing of an object showing all the forces that are acting on it

Applied Force (Fapp)

A force that results when one object pushes or pulls on another object.

motion

An object's change in position relative to a reference point.

slope

the steepness of a line on a graph, equal to rise over run; change in y divided by change in x.

acceleration

final velocity - initial velocity/time; slope of a velocity vs time graph

A velocity vs time graph showing constant speed, no acceleration

A horizontal line

A velocity vs time graph showing acceleration

a straight line with positive or negative slope

average speed

total distance divided by total time traveled

instantaneous speed

the speed of an object at one instant of time (What shows on the speedometer)

velocity

the speed of an object and the direction of its motion

formula for velocity

V = d/t (include a direction)

Momentum

mass x velocity (p=mv)

15 cm/s

An ant travels 75 cm in 5 s. What was the ant's average speed?

36,000 kg m/s

A car with a mass of 1,200 kg has a velocity of 30 m/s west. What is the car's momentum?

Which has a greater momentum: a 45 kg wagon moving 1.5 m/s or a 20 kg animal moving at a velocity of 8 m/s?

The 20 kg animal moving 8 m/s has a greater momentum than the 45 kg wagon moving 1.5 m/s.

A 80-kg mass has an acceleration of 5.5 m/s² north. What is the net force applied?

440 N

If you are pushing on a box with a force of 20 N to the right and there is a force of 7 N left on the box due to sliding friction, what is the net force on the box?

13 N right

9.8 m/s²

What is the acceleration due to gravity on Earth?

What is the slope of a velocity vs time graph?

acceleration

What is the acceleration during part A of the graph? (Hint: slope)

2 m/s²

0 m/s²

What is the acceleration during part B of the graph? (hint: slope)

What is the weight of a 5.5 kg cat on Earth? (Hint: Weight is not the same thing as mass. Use Weight formula.

53.9 N

0

What is the acceleration of an object traveling at the same (constant) velocity?

What would cause a decrease in the gravitational force between two object?

increase the distance between the objects

If a moving basketball directly strikes a basketball at rest, what should happen?

The momentum of the moving basketball is transferred to the other ball. The first basketball stops, the other basketball moves.

How does the mass of an object affect its acceleration?

The greater the mass of the object, the less the acceleration.

When a large moving marble directly strikes a small stationary marble, what happens?

both move forward

When a small moving marble strikes a stationary large marble, what happens?

one moves forward and the other bounces backward

An object at constant velocity will remain at constant velocity if it has

balanced forces acting upon it

An object will accelerate if it has

unbalanced forces acting upon it

What is the net force acting on the rope if there is a 400 N applied force to left and a 300 N applied force to the right?

100 N left

What is the net force acting on an object if there is a 10 N force leftward and a 10 N force rightward?

0 N, balanced forces

velocity

slope of a distance vs time graph

weight

(mass)(acceleration due to gravity); this is a force

unit of velocity

m/s

unit of acceleration

m/s²

Law of Conservation of Momentum

the total momentum of two objects before they collide equals the total momentum of the two objects after they collide

Free Body Diagram

a diagram of all the forces acting on an object; arrows show direction and magnitude of the forces

4800 m

A drone is traveling 72 km/hour. How many meters will it go in 4.0 minutes?

3.5 min

A runner is running at a constant speed of 4.8 m/s. How many minutes does it take the runner to travel 1.0 km?

22 m/s

Find the speed in meters per second of a baseball thrown 38 m from third base to first base in 1.7 s.

the gravitational force is greater; weighs more than on Earth

Jupiter is much more massive than Earth. How does the gravitational force between an object near the surface of Jupiter compare to that object near the surface of Earth?

the gravitational force is less; weighs less than on Earth;

The moon is much less massive than Earth. How does the gravitational force between an object near the surface of the moon compare to that object near the surface of Earth?

0.09 m/s

A 0.015 kg marble moves to the right at 0.225 m/s makes a head on collision with a 0.03 kg marble moving to the left at 0.180 m/s. After the collision, the smaller marble moves to the left at 0.315 m/s. What is the velocity of the 0.03 kg marble after the collision? Hint: use the Law of Conservation of Momentum

free body diagram of an object with 4 forces acting upon it; accelerating to the right

free body diagram of an object with 2 unbalanced forces acting upon it; accelerating upward

Car A

Which car has the greatest acceleration?

-2 m/s²

What is the acceleration from 9 s to 12 s?

Car D

Which car has the greatest mass?

A 4 kg ball moving eastward at a speed of 5 m/s strikes a 2 kg ball at rest. After the collision, the 2 kg ball has a speed of 6.67 m/s. What is the speed of the 4 kg ball? hint: use the law of conservation of momentum

1.67 m/s

What would cause the gravitational force between two objects to increase?

greater mass of one or both of the objects; ex: bigger planet