Motion and Forces

Motion and Forces

Review of Concepts

Motion

Position is relative to an origin

It is usually equal to zero

Position is not the same as distance

Multiple Choice

Which is true about position and distance?

• Distance is positive, while position can be positive or negative

• Distance can be positive or negative, position can only be positive

• Distance and position are both the same.

Speed and Velocity

• Speed = Distance/Time

• When you divide the total distance of a trip by time you get the average speed

• Distance and displacement are not the same

• Instantaneous Speed is the actual speed at a given moment.

Multiple Choice

How far do you go if you drive for 3 hours at a speed of 60 miles per hour?

• 20 miles

• 180 miles

• 20 mph

• 180 mph

Multiple Choice

You drive for 4 hours a distance of 1600 kilometers. What is your speed?

• 40 mph

• 400 km/hr

• 400 km

• 6400 km

Vectors and Velocity

Distance is either zero or positive value

Velocity is speed with direction

Velocity is a vector, while speed is scalar

Each change in position is added up using positive and negative numbers.

Multiple Choice

What is the displacement of the runner from home to second base?

• 180 ft

• 307 ft

• 90 ft

• 127 ft

Multiple Choice

A train travels 50 km/hr heading east to reach a town in 4 hours. The train then reverses and heads west at 25 km/h for 2 hours. What is the train's position now?

• 250 km East

• 150 km East

• 250 km West

• 150 km West

Graphs of Motion

Constant speed means the speed stays the same

Constant speed will look different on a position vs. time graph and a speed vs. time graph

Multiple Choice

What does the horizontal line represent in this graph?

• Resting, not moving

• a constant speed

• acceleration

• velocity

Multiple Choice

What is represented in this graph?

• Return to origin

• negative acceleration

• constant speeding up

• change in direction

Acceleration

• In a speed vs. time graph the line slopes up

• In a position vs. time graph it will curve

• A= Final Velocity - Beginning Velocity/time

• Acceleration can be positive or negative

Review of Forces

Forces

• A force is a push or pull, or an action that has the ability to change motion.

• There are four fundamental forces - gravity, weak force, electromagnetic and strong nuclear force

Multiple Choice

Of the four fundamental forces, which is the weakest?

• Strong nuclear force

• electromagnetic

• weak force

• gravitational force

Forces

• Measured in Newtons

• Can be in direct contact (tensional, applied, etc.)

• or action at a distance (gravity, electric, magnetic)

• Weight depends on mass and gravity

Friction

• Friction is a force that resists the motion of objects or surfaces.

• Different types of Friction

• Rolling, sliding, fluid friction, and static friction.

• Friction depends on both of the surfaces in contact

Multiple Choice

You can get rid of friction completely

• True

• False

Friction

• You can reduce friction, but not get rid of all of it

• Some friction is thought of in positive manner

• Treads on tires or grooves in shoes are ways to increase friction.

Net Forces

• Equilibrium and balanced have a net force of zero newtons

• Equilibrium means that there is no movement

• Unbalanced forces have acceleration

Multiple Choice

What is the net force of the following picture? what direction will it go?

• 0 N, no movement

• 20 N, to the right

• 20 N to the left

• 140 Newtons to the right