Activity 1: Newton’s First and Second Laws of Motion
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Directions: Review the first two Laws of Motion and their mathematical formulas below. Then, complete the math questions following. Be prepared to share your answers.
Newton's First Law of Motion states that a body at rest will remain at rest unless an outside force acts on it and a body in motion at a constant velocity will remain in motion in a straight line unless acted upon by an outside force.
If a body experiences an acceleration (or deceleration) or a change in direction of motion, it must have an outside force acting on it; outside forces are sometimes called net forces or unbalanced forces.
The property that a body has that resists motion if at rest, or resists speeding or slowing up, if in motion, is called inertia. Inertia is proportional to a body's mass, or the amount of matter that a body has. The more mass a body has, the more inertia it has.
The Second Law of Motion states that if an unbalanced force acts on a body, that body will experience acceleration ( or deceleration), that is, a change of speed.
One can say that a body at rest is considered to have zero speed, (a constant speed). So any force that causes a body to move is an unbalanced force. Also, any force, such as friction, or gravity, that causes a body to slow down or speed up, is an unbalanced force. This law can be shown by the following formula:
F= ma
- F is the unbalanced force
- m is the object's mass
- a is the acceleration that the force causes
If the units of force are in newtons, then the units of mass are kilograms and the units of acceleration are m/s2. If the units of force are in pounds (English), then the units of mass are in slugs, and the units of acceleration are ft/s2.
Motion of an object that is not accelerated (moving at a constant speed and in a straight line) can be found using the formula
d= v t
- d is the distance traveled
- v is the rate of motion (velocity)
- t is the time
Questions:
- If a car is traveling at 50 km/hr along a straight line, how many meters does it travel in 10 seconds?
- A force of 5000 newtons is applied to a 1200 kg car at rest. What is its acceleration?
- A 10 kg body has an acceleration of 2 m/s2. Find the net force acting on the body.
- An empty truck with a mass of 2500 kg has an engine that will accelerate at a rate of 1.5 m/s2. What will be the acceleration when the truck has an additional load of 1500 kg ?
- A box resting on a table has a mass of 5.0 kg.
- What is its weight?
- What will be its acceleration when an unbalanced horizontal force of 40 newtons acts on it?
- If the speed of sound on a particular day is 343 m/s, and an echo takes 2.5 seconds to return from a cliff far away, can you determine how far the cliff is from the person making the sound?