<em>Tension,</em> <em>stress,</em> and <em>pressure</em> are nouns. <em>Tense</em> is an adjective meaning <em>under tension.</em>
First, I will speak about physical objects. <em>Tension</em> means pulling or stretching on something long and thin, like a rope, or a wire, or a cable.
<em>Two teams were pulling on a rope playing tug-of-war. They put tension on the rope.</em>
<em>This monofilament fishing line is rated 90 kg test. If you put it under more than 90 kg of tension, it will break.</em>
<em>Pressure</em> means applying a pushing force over an area, possibly tending to crush something or to inflate something. In engineering, it is measured in <em>pascals</em> or <em>psi (pounds per square inch).</em>
<em>The sticker on my car door says that the tires should be inflated to a pressure of 200 kPa.</em>
<em>Submarines that dive too deep can be crushed by the pressure of the water.</em>
<em>Reinforced concrete is very strong because the concrete resists compression and the steel reinforcing bars resist tension.</em>
<em>Stress</em> refers to a bending or twisting force.
<em>"My feet just kept hurting more and more. The doctor said the impact from running had put the bones in my foot under stress, and had caused tiny stress fractures."</em>
When speaking of human emotions, <em>stress</em> and <em>pressure</em> are similar. <em>Pressure</em> suggests time.
<em>"I'm working under a lot of pressure right now, we have to finish the project by the end of the month."</em>
<em>Stress</em> means more generally that you cannot relax or feel good, something is always irritating you.
<em>"The pandemic is causing all kinds of stress. There is financial stress because I'm not working. The kids are at home and they are driving me crazy. And I worry about getting stick myself."</em>
<em>Tension</em> often refers to a difficult personal situation between two people who want two different things. They are figuratively "pulling in different directions."
<em>"Jim and Joan did not look happy. You could see the tension between them. They had come to a difficult point in their marriage. Jim wanted to stay in Chicago, Joan wanted to move to Spokane."</em>